--- title: Modernising legacy systems in UK banking and financial services teaser: Software modernisation in banking and finance goes beyond replacing old code. It’s about navigating a risk-averse environment to transform everything from processes to culture. Here’s what we’ve learned about making it all work. tags: finance,ai,compliance author: - Bethan Ashley - Rob Whittaker - Sami Birnbaum - Michelle Taute published_on: 2026-11-12 --- Modernising legacy systems in UK banking and financial services requires striking a balance between driving rapid innovation and remaining dependable, secure, and fully compliant. That makes it about far more than updating your code base. You’re navigating a heavily regulated, risk-averse environment while being asked to move faster. It can be tempting to stay with systems that (mostly) work, but software is like a garden: without regular tending, it’s hard to grow anything new. Legacy modernisation can improve code quality, overhaul cumbersome processes, enable AI readiness, and even strengthen your engineering culture, making the next code change or big idea easier to execute. Here’s what we’ve learned about creating a successful path to software modernisation. ## How to choose a UK financial software modernisation partner First things first. When you start comparing financial software development companies, you’ll find plenty of potential partners with experience in your tech stack and even some who’ve solved the exact same technology problem you’re facing right now. But it’s much harder to find a partner who staffs your project with developers who go beyond addressing the tickets crossing their desks each week. No problem’s ever the same twice, so you need a software modernisation team like the [thoughtbot London agency](https://thoughtbot.com/london) that’s adaptable, curious, and kind, yet not afraid of hard conversations. Our senior teams dig deeper to understand the bigger picture - across people, processes and code - to create impact that lasts beyond any single consulting engagement. Your internal team will come away with new engineering and business practices that help modernise all your future projects. ## Building an engineering culture that supports innovation A big part of creating that long-term change is overhauling your technology culture. Try thinking beyond strict legacy app modernisation to a larger shift that enables your engineering teams to move faster and more securely every day. During our engagements, we leave behind [processes just as valuable as our code](https://thoughtbot.com/blog/don-t-hire-thoughtbot-to-write-code). Many highly regulated financial institutions, for example, lack modern version control and rely on both manual deployment and manual quality assurance. We’ll embed with teams to work on using git with detailed commit notes (instant documentation), moving to continuous deployment, and creating automated test suites. Improved communication is another area of focus. Shifting conversations from direct messages to open forums builds trust and shared understanding. It can also be the start of creating a common set of engineering standards and documentation across different silos within a large company. This adds speed to any project and allows staff to more seamlessly move between teams. ## How can banks integrate AI to modernise financial services? AI is in almost everyone’s strategic plan right now and investing in modernising legacy systems and processes ups your AI readiness. When your engineering team has reliable rollback capabilities, for instance, it reduces risk for future artificial intelligence projects. Automation is another easy win. For an early project, try leveraging AI skills to automate a straightforward task like logging a website into a particular service it needs to access. There are bigger shifts on the AI horizon, too. Right now, users give web apps data through forms (or a series of forms), but in the future, users may simply give a request or command through an agent. You’ll need to approach how you store data differently for agents to understand it, moving from relational databases to storing data as vectors. And you may even need to add additional data layers on a website for agents to understand it. ## How software modernisation supports operational resilience For UK financial services firms, resilience is both an engineering goal and a regulatory requirement. Firms covered by the FCA’s rules must be able to keep important business services within impact tolerances during severe but plausible disruptions. In its [one-year review of operational resilience](https://www.fca.org.uk/publications/good-and-poor-practice/operational-resilience-insights-observations-one-year), the FCA urged firms to go beyond compliance and build resilience into how they design products and services. Modernisation can help make that shift practical. Modern engineering practices make systems and their dependencies easier to understand, helping teams find and fix weaknesses sooner. Automated testing can catch problems before they reach customers and give teams more confidence when changing critical systems. Reliable, repeatable deployments reduce the risk of a release causing disruption and make it easier to recover if something goes wrong. Modernisation is also a good time to review how your systems handle personal data. The UK GDPR requires data protection by design and default, so privacy needs to be considered from the design stage and throughout a system’s lifecycle. Addressing it early can also help you avoid costly redesigns later. ## Choosing financial software development services There’s no shortage of legacy modernisation opportunities inside most banks or financial institutions. It might be refactoring legacy code, re-writing an application in a more modern language or aligning on one shared source of truth for data. Even seemingly mundane things, such as a web form, can present an opportunity for major improvement. For one banking client, thoughtbot turned a single form handling a dozen different loan application types into a dozen different forms. This meant each form only collected the necessary data for that workstream, simplifying business decisions and reducing cognitive load for both humans and AI agents. One overlooked area for investment? Adding [product design](https://thoughtbot.com/services/product-design) to your development team to improve the overall user experience. While it can seem like an added cost, this addition can make your app easier to navigate, reduce customer service calls, build trust and help you stack up against modern consumer apps. A modern app design may also open new markets and sway younger customers your way. Ready for financial services or banking modernisation? Partner with our senior teams to innovate while reducing risks. [Let’s talk.](https://thoughtbot.com/industries/fintech)