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Tier 1 Investment bank based in Canary Wharf.

Role - C# Developer - Desktop Applications

Duration - 6 months with likely extension

Rate - £416 p/d (inside IR35)

Location - Hybrid / Canary Wharf

Tech Stack

C#WPFWinformsJavascriptSQLOracle

Tasks

Tasks range from understanding business requirements, designing application structures, business data analysis, programming WPF (Windows Presentation Foundation) applications in Visual C#.NET on both Oracle and SQL Server database, testing with users, implementation through Development, Quality Assurance (QA), Production and Disaster Recovery environments. Supporting users and writing operation documents including User Helps (manuals) will also be required.As well as application development, this role will also include all aspects of system constructions and support for existing programmes which are written as WinForms (C#.NET) applications. Also, applications written in other languages like MS VBA for Excel and Access, MS VB and MS Excel Macros will also be required.

Additional Tasks

Defining Database objects required in systems to connect with SQL and Oracle Database Administrators in both London and New York.Providing script for database inquiry languages, i.e., T-SQL (SQL Server) and PL/SQL (Oracle) to perform data analysis based on requirements from business parties.Setting up a system distribution method to Citrix and application servers for both Web and Window applications.Troubleshooting systems in an event of failure and implementing necessary solutions by checking Windows Operating System, Internet Information Server and any other relevant environments where the applications are running. In some case this role will act to liaise with other application support team staff.Following the existing team programming policy to keep a common development style to be shared in team members.Updating versions of MS .Net Framework and MS Visual .NET platform to include any necessary changes of existing systems running in Production.Liaising with the relevant support teams such as other Development sections, Technical Support, Network and Infrastructure and DBA where Business users experience system problems.Assessing the impact of data processing loads on SQL and Oracle database and, when appropriate, finding alternative approaches.Rolling out changes with a coordination of Release manager. It is important to maintain the change history of applications

GCS is acting as an Employment Business in relation to this vacancy.

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Senior Full-Stack Developer

About the role

This is a hands-on senior position where you'll play a key role in shaping the technical direction of a growing product. You'll combine architecture and technical leadership responsibilities with active software development, working closely with the product and stakeholders.

What you'll do

Take end-to-end technical ownership of a core product, from architecture through to delivery and ongoing evolution.Help drive technical decision-making and contribute to scalable, maintainable system design.Build and maintain applications across the full technology stack, including backend services, frontend experiences, APIs, and third-party integrations.Support the transition of platform knowledge from external partners to the internal team, ensuring long-term ownership and sustainability.Establish and promote engineering best practices while mentoring and supporting other developers.Collaborate with stakeholders and end users to understand product usage, identify challenges, and translate business needs into technical solutions.Work closely with product and design teams to help shape the product roadmap and user experience.

Must have

6+ years of professional software development experience.Strong experience building and maintaining modern web applications across both frontend and backend environments.Proficiency in modern programming languages and frameworks used for full-stack development.Experience designing scalable, maintainable software systems and contributing to application architecture.Proven ability to lead technical discussions and make architectural decisions.Comfortable balancing hands-on development with technical leadership responsibilities.Experience working with APIs, integrations, and distributed systems.Familiarity with containerization technologies and cloud-based development practices.Experience working with relational databases and data modeling.

Should have

Experience with cloud platforms and modern software delivery practices, including automation, CI/CD, infrastructure management, and monitoring.Knowledge of Dutch or French, in addition to English.

Nice to have

Exposure to multiple programming languages, frameworks, or technology ecosystems.Experience working in regulated industries such as financial services, compliance, healthcare, insurance, or similar domains.Experience scaling products in a high-growth or startup environment.

GCS is acting as an Employment Agency in relation to this vacancy.

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Full Stack Developer (Contract)

Location: Remote (UK)
Contract Length: 6 Months
Day Rate: £400 per day OUTSIDE IR35
Tech Stack: C#, SQL, Vue.js

Overview

We are seeking an experienced Full Stack Developer to support the re-engineering and modernisation of a core business platform. The successful candidate will play a key role in migrating an existing application from .NET Framework 4.1 to .NET 10, helping to improve performance, scalability, maintainability and cloud readiness.

Working within an agile development team, you will contribute across the full software development lifecycle, from architecture and design through to development, testing and deployment.

Key Responsibilities

Redevelopment and modernisation of an existing platform from .NET Framework 4.1 to .NET 10.Design, develop and maintain scalable web applications using C#, SQL Server and Vue.js.Collaborate with business stakeholders, architects and developers to define technical solutions.Refactor legacy code and implement modern development practices.Develop and consume RESTful APIs and backend services.Optimise database performance and maintain SQL Server environments.Participate in code reviews, testing and release activities.

Essential Skills & Experience

Strong commercial experience developing applications using C#.Experience with SQL Server, including:Proven experience developing front-end applications with Vue.js.Experience working on full software development lifecycle projects.Demonstrable experience modernising or upgrading legacy applications.

Desirable Skills

Experience with Microsoft Azure services.Knowledge of Azure DevOps and CI/CD pipelines.Experience containerising applications using Docker and Kubernetes.Experience with microservices architecture.Exposure to Entity Framework Core.

Ideal Candidate

Comfortable working in a fast-paced project environment.Proven track record of delivering platform modernisation projects.Able to work independently whilst collaborating effectively within a wider team.Strong attention to detail with a focus on quality and maintainability.

Technical Environment

.NET Framework 4.1 → .NET 10 MigrationC#SQL ServerVue.jsAzure (desirable)

GCS is acting as an Employment Business in relation to this vacancy.

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Global bank based in Canary Wharf.

Role - C# Developer - Desktop Applications

Duration - 6 months with likely extension

Rate - £416 p/d (inside IR35)

Location - Hybrid / Canary Wharf

Tech Stack

C#WPFWinformsJavascriptSQLOracle

Tasks

Tasks range from understanding business requirements, designing application structures, business data analysis, programming WPF (Windows Presentation Foundation) applications in Visual C#.NET on both Oracle and SQL Server database, testing with users, implementation through Development, Quality Assurance (QA), Production and Disaster Recovery environments. Supporting users and writing operation documents including User Helps (manuals) will also be required.As well as application development, this role will also include all aspects of system constructions and support for existing programmes which are written as WinForms (C#.NET) applications. Also, applications written in other languages like MS VBA for Excel and Access, MS VB and MS Excel Macros will also be required.

Additional Tasks

Defining Database objects required in systems to connect with SQL and Oracle Database Administrators in both London and New York.Providing script for database inquiry languages, i.e., T-SQL (SQL Server) and PL/SQL (Oracle) to perform data analysis based on requirements from business parties.Setting up a system distribution method to Citrix and application servers for both Web and Window applications.Troubleshooting systems in an event of failure and implementing necessary solutions by checking Windows Operating System, Internet Information Server and any other relevant environments where the applications are running. In some case this role will act to liaise with other application support team staff.Following the existing team programming policy to keep a common development style to be shared in team members.Updating versions of MS .Net Framework and MS Visual .NET platform to include any necessary changes of existing systems running in Production.Liaising with the relevant support teams such as other Development sections, Technical Support, Network and Infrastructure and DBA where Business users experience system problems.Assessing the impact of data processing loads on SQL and Oracle database and, when appropriate, finding alternative approaches.Rolling out changes with a coordination of Release manager. It is important to maintain the change history of applications

GCS is acting as an Employment Business in relation to this vacancy.

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GCS is acting as an Employment Agency in relation to this vacancy.

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Integration Design:
Collaborate with business stakeholders, IT teams, and external partners to gather integration requirements and define workflows. Design data mappings, transformations, APIs, and message schemas to facilitate the secure and efficient exchange of data between systems.Development and Implementation:
Design, develop, test, and deploy integration solutions using C#, .NET, or similar programming languages. Build RESTful APIs and backend services to support integration needs. Configure connectors and implement robust error handling and retry mechanisms to ensure reliability and data integrity.Integration Platforms and Tools:
Utilize integration platforms such as Azure Logic Apps, Azure Data Factory, SSIS, or other middleware tools to orchestrate data flows and integrate diverse systems. Experience with tools such as Postman, Swagger, and API gateways is highly desirable.API and Service Integration:
Build and maintain APIs (REST and/or SOAP), working with authentication, authorization, and secure data exchange. Integrate internal and third-party APIs to facilitate service-oriented and event-driven architecture across systems.Data Transformation and Mapping:
Implement data transformation logic to convert between formats like JSON, XML, and CSV. Design reusable components and mappings to streamline data flow between systems with different schemas or protocols.Testing and Debugging:
Perform unit, integration, and end-to-end testing of integration workflows and APIs. Debug issues using tools such as Fiddler, Postman, and application logs. Continuously optimize performance and reliability through code refactoring and system tuning.Documentation and Reporting:
Document API contracts, integration configurations, and solution architecture to support maintainability. Provide progress updates, technical summaries, and risk reports to stakeholders throughout the project lifecycle.Collaboration and Communication:
Work closely with software developers, data engineers, QA teams, and business analysts to align integration work with broader project goals. Clearly communicate technical designs, project updates, and roadblocks to both technical and non-technical stakeholders.Continuous Learning:
Keep up-to-date with integration frameworks, cloud technologies, and development best practices. Actively participate in knowledge-sharing sessions and contribute to the continuous improvement of integration standards and code quality.

GCS is acting as an Employment Business in relation to this vacancy.

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Tier 1 bank based in Canary Wharf.

Role - C# Developer - Desktop Applications

Duration - 6 months with likely extension

Rate - £416 p/d (inside IR35)

Location - Hybrid / Canary Wharf

Tech Stack

C#WPFWinformsJavascriptSQLOracle

Tasks

Tasks range from understanding business requirements, designing application structures, business data analysis, programming WPF (Windows Presentation Foundation) applications in Visual C#.NET on both Oracle and SQL Server database, testing with users, implementation through Development, Quality Assurance (QA), Production and Disaster Recovery environments. Supporting users and writing operation documents including User Helps (manuals) will also be required.As well as application development, this role will also include all aspects of system constructions and support for existing programmes which are written as WinForms (C#.NET) applications. Also, applications written in other languages like MS VBA for Excel and Access, MS VB and MS Excel Macros will also be required.

Additional Tasks

Defining Database objects required in systems to connect with SQL and Oracle Database Administrators in both London and New York.Providing script for database inquiry languages, i.e., T-SQL (SQL Server) and PL/SQL (Oracle) to perform data analysis based on requirements from business parties.Setting up a system distribution method to Citrix and application servers for both Web and Window applications.Troubleshooting systems in an event of failure and implementing necessary solutions by checking Windows Operating System, Internet Information Server and any other relevant environments where the applications are running. In some case this role will act to liaise with other application support team staff.Following the existing team programming policy to keep a common development style to be shared in team members.Updating versions of MS .Net Framework and MS Visual .NET platform to include any necessary changes of existing systems running in Production.Liaising with the relevant support teams such as other Development sections, Technical Support, Network and Infrastructure and DBA where Business users experience system problems.Assessing the impact of data processing loads on SQL and Oracle database and, when appropriate, finding alternative approaches.Rolling out changes with a coordination of Release manager. It is important to maintain the change history of applications

GCS is acting as an Employment Business in relation to this vacancy.

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Global bank based in Canary Wharf.

Role - C# Developer - Desktop Applications

Duration - 6 months with likely extension

Rate - £416 p/d (inside IR35)

Location - Hybrid / Canary Wharf

Tech Stack

C#WPFWinformsJavascriptSQLOracle

Tasks

Tasks range from understanding business requirements, designing application structures, business data analysis, programming WPF (Windows Presentation Foundation) applications in Visual C#.NET on both Oracle and SQL Server database, testing with users, implementation through Development, Quality Assurance (QA), Production and Disaster Recovery environments. Supporting users and writing operation documents including User Helps (manuals) will also be required.As well as application development, this role will also include all aspects of system constructions and support for existing programmes which are written as WinForms (C#.NET) applications. Also, applications written in other languages like MS VBA for Excel and Access, MS VB and MS Excel Macros will also be required.

Additional Tasks

Defining Database objects required in systems to connect with SQL and Oracle Database Administrators in both London and New York.Providing script for database inquiry languages, i.e., T-SQL (SQL Server) and PL/SQL (Oracle) to perform data analysis based on requirements from business parties.Setting up a system distribution method to Citrix and application servers for both Web and Window applications.Troubleshooting systems in an event of failure and implementing necessary solutions by checking Windows Operating System, Internet Information Server and any other relevant environments where the applications are running. In some case this role will act to liaise with other application support team staff.Following the existing team programming policy to keep a common development style to be shared in team members.Updating versions of MS .Net Framework and MS Visual .NET platform to include any necessary changes of existing systems running in Production.Liaising with the relevant support teams such as other Development sections, Technical Support, Network and Infrastructure and DBA where Business users experience system problems.Assessing the impact of data processing loads on SQL and Oracle database and, when appropriate, finding alternative approaches.Rolling out changes with a coordination of Release manager. It is important to maintain the change history of applications

GCS is acting as an Employment Business in relation to this vacancy.

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C# Developer Role - Hybrid / Liverpool street - 6 month Contract - Banking

Role - C# Developer (T/SQL, PL/SQL)

Duration - 6 months with very likely extension

Location - Hybrid / Liverpool Street (London) - 3 days per week in a Liverpool Street office

Rate - £690 per day (Inside IR35)

Tech Stack

C#SQLOracle

Tasks

Tasks include understanding business requirements, designing applications, business data analysis, programming in Visual C#.NET using both Oracle and SQL Server database, Unit testing, Quality Assurance (QA), Implementation, Production and Disaster Recovery environments supporting users and preparing documents.Along with the application development, this role will also include supporting the existing C# and .NET applications. General IT Support to maintain environmentDefining database objects required in the systems. Interactions with the SQL and Oracle Database Administrators in both London and New York.Providing script for database enquiry languages, i.e., T-SQL (SQL Server) and PL/SQL (Oracle) so that data analysis can be performed based on requirements from relevant business parties.Support setting up a system distribution method for Citrix and application servers for both Web and Window applications.Troubleshooting systems in the event of failure and implementing solutions (Code fix, SQL scripting etc), including checking Windows Servers, Databases (SQL Server or Oracle) and any other relevant environments where the system is running. In some cases, this will involve liaising with other application support team staff across London and New York offices.Following the development teams' programming policy and procedures to maintain common programming practice.Updating versions of MS .Net Framework and MS Visual .NET platform to include any necessary changes of the existing systems running in Production environment.`Liaising with the relevant support teams such as other Development team sections, Technical Support, Network and Infrastructure and DBAs whenever Business users experience system problems.Assessing the impact of data processing loads on SQL and Oracle databases and when appropriate, finding alternative solutions.Actively assisting rolling out changes through coordination with the Release team. It is also very important to maintain the change history of the applications.Communicating with primary support Helpdesk staff in London and New York to provide the necessary system supports.

GCS is acting as an Employment Business in relation to this vacancy.

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Join a leading global banking client on a major Identity & Access Management (IAM) transformation programme.

We're looking for an IAM-focused Developer with strong experience building secure identity solutions, cloud-native applications, and event-driven services

IAM Application Developer | Python | GCP | Banking
📍 London or Sheffield (Hybrid)
📅 6-Month Contract
🏦 Global Banking Environment

✅ Strong IAM experience is essential
✅ Python and cloud-native development background required
❌ Not suited to Java-heavy profiles

💡 Key Skills:
* IAM / Identity Life cycle Management
* Python Development
* REST APIs & Microservices
* Google Cloud Platform (GCP)
* Pub/Sub & Event-Driven Architecture
* OAuth2, OIDC, JWT, SAML
* Terraform / Infrastructure as Code
* Identity Orchestration (Auth0, Okta, WorkOS or similar)
* React & TypeScript (desirable)

🔹 You'll be:
* Building and securing identity APIs
* Developing IAM automation and provisioning workflows
* Creating cloud-native applications and event-driven services
* Working closely with Security, DevOps, and Engineering teams

Interested? Apply now or get in touch for more details.

GCS is acting as an Employment Business in relation to this vacancy.

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