How a relationship‑led UK bank reduced legacy risk and unlocked scalable growth

A relationship‑led UK bank wanted to fundamentally modernise and migrate away from a heavily customised mainframe that had supported its branch‑focused model for decades but was now holding back growth. Change was slow, resilience expectations were rising and specialist knowledge was concentrated among a shrinking group of experts. The bank set a clear ambition: remove material legacy infrastructure and reduce operational risk, improve agility and prepare for long‑term expansion without compromising the personalised service that defined its brand. 

Setting a path to reduce risk and enable growth

The bank recognised that its deeply embedded legacy core – shaped through years of bespoke development – limited its ability to innovate at pace. It also increased dependency on niche expertise and made meeting regulatory expectations around availability, continuity and resilience more challenging across the full value chain, from customer interaction through to core processing. 

To create a credible route forward, the bank partnered with Baringa to validate its technology strategy and roadmap, define end-to-end transition states and set out how full front-to-back modernisation, underpinned by a cloud‑ready platform could support its growth plans.  

Designing a scalable, cloud‑ready architecture

Working closely with teams across the bank, our work spanned enterprise architecture, core banking, payments, data and cloud strategy, creating a coherent front-to-back target architecture rather than a series of point solutions. We helped shape the future architecture so the organisation could progressively migrate from a monolithic mainframe to a modular, domain‑based design.

This work included: 

• Setting a bank‑wide capability and logical enterprise architecture aligned to an industry standardized architectural model, Banking Industry Architecture Network (BIAN) 

• Shaping the core banking and payments applications, integration and data architectures 

• Defining clear transition state architectures to guide multi‑year change 

• Developing the mainframe migration and decomposition approach utilising accelerators from similar large‑scale programmes 

Strengthened governance forums clarified decision rights, controlled technical debt and supported delivery as the programme progressed from design into execution. 

Creating a cloud strategy that met operational, regulatory and security needs

The bank needed confidence that cloud strategy could support the migration of critical banking applications while meeting the strict requirements of operational resilience and information security. We led the options analysis through to board approval, balancing regulatory constraints with the ambition for agility, modern engineering and long‑term scalability. 

Breaking the monolith and enabling modular services

We designed the approach to systematically decompose the mainframe into modular services with clear domain boundaries and modern integration patterns. This created a foundation that supports faster change cycles, improved resilience and the ability to scale bespoke products while staying true to the bank’s relationship‑led ethos. 

To support delivery at pace, we also: 

• Supported vendor selection to select fit‑for‑purpose Commercial Off-The Shelf (COTS) components to replace mainframe functionality 

• Mobilised programme teams with the right cadence, tooling and governance to manage the complexity of a live core migration 

A clear path to resilience and long‑term growth

The bank now has a credible roadmap to significantly reduce legacy mainframe and key‑person risk while improving resilience and continuity. Its modern, cloud‑ready architecture enables faster time‑to‑market for new propositions and provides a scalable foundation for its five‑year growth plan. 

Most importantly, this highly complex and differentiated transformation will allow the bank to continue delivering the local, relationship‑driven service that sets it apart – now supported by a future ready technology backbone ready built for scale. 

Need to modernise legacy core platforms for resilience and growth?

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