Senior Software Engineer

Senior Software Engineer – C#

London, UK

£140,000 basic + bonus

You’ll be the go-to engineer for C# performance, database optimisation, and high-throughput system tuning . This role is all about deep technical ownership: improving query performance, reducing GC pressure, tightening memory usage, and ensuring systems run fast, stable, and scalable under heavy load.

If you enjoy tearing apart slow code, rewriting inefficient queries, and re-architecting components to squeeze out every millisecond, this is the role for you.

What you’ll be doing

• Profiling and optimising C#/.NET code with a focus on memory, CPU usage, and GC behaviour
• Rewriting and tuning SQL queries, indexing strategies, and schema design to improve speed and reduce load
• Designing and implementing performance enhancements across high-volume, low-latency production systems
• Building and maintaining automated performance, load, and stress-testing frameworks
• Working closely with Engineering and Product teams to diagnose issues and meet strict performance targets
• Mentoring engineers on best practices for efficient C# coding, async programming patterns, and database performance
• Influencing architectural decisions with a strong bias toward speed, resilience, and scalability

What we’re looking for

• Senior-level experience with C#/.NET in production, ideally on high-performance or distributed systems
• Strong experience optimising SQL databases (Postgres, SQL Server, or similar)
• Proven track record profiling, debugging, and tuning GC, memory allocation, and concurrency
• Fluency with profiling tools (dotTrace, PerfView, JetBrains tools, SQL Profiler, etc.)
• Experience building scalable systems in containerised or cloud environments (Docker, Kubernetes, AWS/Azure)
• Familiarity with load-testing tools (k6, JMeter, Gatling) and monitoring/observability stacks
• Clear communicator comfortable working with both technical and non-technical teams

What’s on offer

• A performance-driven engineering culture where improvement is visible and measurable
• Complex problems that genuinely move performance metrics when solved
• Strong influence on architecture, implementation, and engineering best practices
• Central London hybrid working
• Up to £140,000 basic + leading bonus scheme

Tech Stack

C#, .NET, Postgres, SQL Server, Python, Java, Kubernetes, Docker, AWS, Azure, k6, JMeter, Gatling

If you excel at making fast systems even faster and want to work on performance-critical software, we want to hear from you