Pioneering a new generation of savings in the UK with Mambu
Building on a five-year partnership with Mambu, Paragon Bank launched Spring Savings to tackle one of the UK savings market’s biggest inefficiencies: inertia. The mobile-first savings app reached tens of thousands of customers and £800 million in deposits within eight months, proving that a simpler, transparent approach can motivate savers to move their money and earn better returns.
- £0m
- in deposits within eight months
- £0bn
- in deposit aggregator balances hosted on Mambu
Paragon Bank
About the customer
Established in 1985, Paragon Bank is a leading UK specialist lender and FTSE-listed bank that has matured into an influential player in UK financial services over its 40-year heritage. After receiving its banking license in 2014, the group launched its savings franchise to support its lending activities. Growing from zero to £16 billion in deposits over a decade, Paragon now uses these deposits to fuel the UK economy by lending to buy-to-let landlords and businesses of all sizes, supporting the ambitions of people across the country.
As part of its digital evolution, Paragon launched Spring Savings, a mobile-first savings app designed specifically for people who leave money sitting in current accounts earning little to no interest. Spring operates as a transparent, digital-first brand that allows customers to benefit from competitive rates without the complexity of switching their primary bank.
The challenge
Overcoming savings inertia
Despite a highly competitive market, Paragon identified over £300 billion sitting in UK current accounts, representing a massive pool of funding that was not generating meaningful returns for consumers. This inertia affects roughly 29 million accounts, with nearly half of UK adults leaving their savings with current account providers out of habit or concern that moving their money would make access more complicated.
To address the challenge of inertia, Paragon designed a savings companion that required a highly flexible and resilient backend. The bank adopted a composable banking architecture with a cloud-native core capable of integrating with external fintech tools.
“There’s a lot of people not being proactive with their savings, and we figured out why, and then we set about building Spring as being the opposite…helping solve the inertia problem.”
- Derek Sprawling, Managing Director of Savings at Paragon Bank
The solution
A best-of-breed composable architecture
Paragon’s partnership with Mambu began in 2020, making Spring the latest milestone in a relationship that now spans more than five years. At the outset, Paragon selected Mambu’s banking engine to support the bank’s deposits aggregator franchise. A year later, the partnership expanded to include Paragon’s Development Finance division, both of which continue to run on Mambu today.
Building on that experience and the familiarity developed within Paragon’s technology teams, the bank considered Mambu’s modern core banking platform the natural foundation for Spring. Serving as the engine for deposit management and account administration, Mambu provided the flexibility required to assemble a modern digital savings proposition.
Underpinned by Amazon Web Services (AWS), this architecture allowed Paragon to plug in specialised solutions for a superior customer experience. The stack included OutSystems for high-performance low-code mobile components, Moneyhub for Open Banking-powered instant transfers, and several dedicated partners for cybersecurity and financial crime prevention.
By connecting these best-of-breed components via a custom middleware layer, Paragon created a solution that offers near-instant transfers and an intuitive, modern interface.
Underpinned by Amazon Web Services (AWS), this architecture allowed Paragon to plug in specialised solutions for a superior customer experience. The stack included OutSystems for high-performance low-code mobile components, Moneyhub for Open Banking-powered instant transfers, and several dedicated partners for cybersecurity and financial crime prevention.
By connecting these best-of-breed components via a custom middleware layer, Paragon created a solution that offers near-instant transfers and an intuitive, modern interface.
“We wanted to build a savings app that was not only functional but also easy to use for our customers. That’s why we were comfortable sticking with Mambu because we could see how we would plug into the system and make sure the end solution was as we envisioned it.”
- Derek Sprawling, Managing Director of Savings at Paragon Bank
The implementation
Phased rollout and technical precision
The implementation journey prioritised quality and real-world validation over speed. While the technical build took less than two years, Paragon spent significant time refining policy decisions regarding liquidity management, financial crime considerations, and onboarding flows to ensure Spring delivered the right experience from the start.
This meticulous process involved a phased rollout, beginning with internal staff and "friends and family" pilots before the full public launch in April 2025.
Leveraging Mambu’s configuration capabilities rather than complex custom coding, Paragon's team built the expertise to manage the platform effectively. To achieve the bank’s vision of providing the best experience to its customers, over 10 new partners were connected to the Mambu composable core to support not just the app, but also a custom-built contact centre portal. This architecture ensured strong operational resilience, allowing the team to monitor system performance in milliseconds and introduce continuous operational refinements as the proposition evolved.
The result
Sustainable growth and future innovation
Since the public launch on Mambu, Spring Savings has prioritised sustainable, high-quality service over short-term price-chasing. This strategy has successfully attracted customers to the reliable long-term savings solution rather than simply chasing the highest rate available at a given moment.
The results are clear. Within eight months of launch, Spring reached £800 million in deposits and tens of thousands of customers by early 2026. By combining an intuitive app UX with a 24/7 virtual assistant and a warm, UK-based human support team in Solihull, Spring has achieved an impressive rating of 4.7 on Trustpilot.
Looking ahead, Paragon plans to build on this momentum by expanding distribution through additional partnerships and product categories in the deposit aggregator space via Mambu, which already hosts ~£4 billion in balances.
The bank also plans to introduce an “invite a friend” feature and launch at least one new savings product in 2026.
The bank also plans to introduce an “invite a friend” feature and launch at least one new savings product in 2026.
Through ongoing service enhancements and a commitment to its human-first digital strategy, Paragon continues to demonstrate how technology and banking expertise can work together to help millions of UK savers achieve better outcomes.
“Our growth strategy with Spring prioritises sustainable, long-term relationships over short-term balance chasing. We’ve grown as planned and we know there is much further to go as we build momentum.”
- Derek Sprawling, Managing Director of Savings at Paragon Bank
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