Senior Kotlin Engineer (XP, GCP) – Investment Banking – London

Senior Kotlin Engineer (XP, GCP) - Investment Banking - London/Hybrid Daily rate: £600 - £800 (inside IR35) Duration: 6 months Start: ASAP My client is looking for an experienced Senior Kotlin engineer to support and extend a cloud-hosted platform used for bookbuilding issuances within Investment Banking Capital Markets. You will join a high-calibre London-based front office engineering team working on a next-generation issuance platform replacing a legacy bookbuilding system. This is a hands-on engineering role with a strong emphasis on Extreme Programming (XP) practices, including mob programming, test-driven development, and continuous refactoring. Engineers are expected to contribute across development, integration, and production support, collaborating closely to maintain high standards of code quality, system reliability, and performance. Required & Desirable Skills Strong commercial experience building backend services using Kotlin Experience with event-sourced and event-driven architectures Deep familiarity with XP practices, including: Mob programming as a primary way of working Test-driven development (TDD) Continuous refactoring and clean code principles Cloud experience with GCP, including: GKE and/or Cloud Run Cloud SQL and Memory store Artifact Registry and Cloud Logging Key Management Experience with CI/CD and SDLC in regulated or enterprise environments Comfortable working on production systems requiring high availability and accuracy Engineers in this role: Work primarily in mobs, sharing ownership of design and code Build, test, and evolve services with a strong focus on clarity, simplicity, and maintainability Support the platform in production, using incidents and defects as opportunities to improve system design and resilience *Rates depend on experience and client requirements