Pontoon is an employment consultancy. We put expertise, energy, and enthusiasm into improving everyone''s chance of being part of the workplace. We respect and appreciate people of all ethnicities, generations, religious beliefs, sexual orientations, gender identities, and more. We do this by showcasing their talents, skills, and unique experience in an inclusive environment that helps them thrive. C# Developer (Architecture Focused) London, 3 days per week on site required6-month initial contract 400.00 via umbrella per day The OpportunityWe''re looking for a senior C# Developer with a strong architectural focus to join a highly skilled engineering team working on business-critical systems at scale. This role sits at the heart of a major technology estate and offers the chance to modernise legacy platforms, shape technical direction, and contribute to secure, high-performance solutions.You''ll work across both transformation initiatives and greenfield development, collaborating closely with engineering, DevOps, DBAs, and governance teams in a structured, enterprise environment.What You''ll Be DoingDesigning and developing applications using .NET Framework / .NET Core, React / TypeScript, Python, and relational databasesRefactoring and modernising legacy systems to reduce technical debt and improve performance and reliabilityEmbedding modern security patterns across APIs and services (authentication, authorisation, OWASP controls, secure access)Contributing to greenfield sol