Building societies keep getting sold the wrong shopping list.
A vendor shows up with a deck. It says "core banking platform." Three slides later, it's showing mobile onboarding screens and Conversational Banking demos. Somewhere in the deck, the actual ledger, where interest gets calculated and balances get held, never comes up.
That confusion costs money. Building societies are member-owned and capital-constrained. Boards want a straight answer to a simple question: are we replacing the ledger, or are we replacing the front end?
Two different layers, one buying decision
A core banking system is the ledger. It holds every account, every balance, every interest calculation, every regulatory reporting feed. Providers like SBS, TCS BaNCS, Mambu, and Temenos live here. Nottingham Building Society's recent move to SBS Core MSS 6.1 is a core banking decision: new mortgage and savings engine, same 300,000 members, different plumbing underneath.
A digital banking platform sits above that ledger. For Backbase, that's the AI-native Banking OS, the Control Plane that coordinates the layer members and staff actually touch: mobile and online banking, the branch and call center workspace, onboarding, servicing. It doesn't hold the ledger. It orchestrates the work around it.
Simon Broadley, now CEO of Furness Building Society (he led this decision as CCO), put the buy-versus-build economics plainly on Banking Reinvented:
"There is now absolute recognition that embracing technology, embracing digital solutions, can perpetuate and amplify the brand that we have as a mutual."
Furness didn't replace its core. It partnered with Backbase for retail savings and onboarding, because building a proprietary front end in-house no longer made sense for a society its size. Backbase calls this buy plus build: license a proven foundation, then build on top for differentiation. That's the decision most building societies actually face: not "which core," but "who runs the member experience on top of the core we already have."
Why this matters more for a building society than a bank
Building societies run on different economics than shareholder banks. No dividend pressure, but no scale to burn on a multi-year core replacement either. Every pound has to protect the member relationship, not just the transaction.
That's why the human-in-the-loop question shows up constantly in this sector. Susanne Parry, COO of Cumberland Building Society, described her organization's approach in an episode on the same podcast:
"We have a phrase which is human led but underpinned by good digital."
She was direct about where automation earns its place: "We've all had really bad AI chat experiences. And that's not helping. That's driving people towards human, actually." For fraud, financial difficulty, or a first mortgage, Cumberland keeps a person in the loop on purpose, not out of habit.
That's a digital banking decision, not a core banking one. A core replacement won't fix broken Conversational Banking. A new mobile app won't fix a broken ledger. Conflating the two is how societies end up buying the wrong thing, or the right thing from the wrong vendor.
A simple way to evaluate vendors
Sort every vendor on the RFP into one of two columns before a single call:
Core banking, the ledger: SBS, TCS BaNCS, Mambu, Temenos. Evaluate on regulatory reporting, product configuration, and migration risk.
Digital banking platform, the digital layer: Backbase, Fintilect, Mutual Vision. Evaluate on member journey quality, staff workspace design, and how much of the human-in-the-loop model you preserve.
Most societies don't need to touch both columns at once. Furness kept its core and modernized the front end. Nottingham modernized its core and kept its service model. The mistake is judging a front-end platform against core banking criteria, or the reverse. Vendor lists like sdk.finance's core banking comparison are useful for the first column. They say nothing about the second.
Where this movement goes next
The UK's Building Societies Association has watched this exact tension play out across its members: tradition versus speed, none of it resolved by picking one vendor category. Backbase's own conversations with mutuals point the same way: neobanks can out-tech a mutual, and big banks can outspend one, but neither can match the depth of relationship a building society already has.
The starting point is simple. Decide which layer you're actually buying before the first vendor call. It's the difference between modernizing on purpose and modernizing by accident.
FAQs
What's the best digital banking platform for building societies?
There's no single best platform for every society. It depends on what you're actually replacing. For the core ledger, SBS, TCS BaNCS, Mambu, and Temenos are the established options. For the digital layer that members and staff touch, Backbase, Fintilect, and Mutual Vision are the ones building societies evaluate most. Most societies need one, not both, at any given time.
What's the difference between a core banking system and a digital banking platform?
A core banking system holds the ledger: accounts, balances, interest, regulatory reporting. A digital banking platform sits above it, running the mobile app, online banking, branch and call center workspaces, and onboarding. One replaces the books. The other replaces what members and staff actually touch.
Is Backbase a core banking platform for building societies?
No. Backbase is the AI-native Banking OS: the Control Plane that sits above the core, coordinating digital channels, front-office workspaces, and operations so members, staff, and AI agents work from the same data. It doesn't replace the ledger. It orchestrates everything a member and a colleague actually touch, and runs alongside a core, not instead of one. For a building society, that means Backbase runs the retail savings journey, onboarding, and the CSR workspace, while SBS, TCS, or whichever core provider the society already runs keeps handling accounts and interest. Furness runs exactly this model today.
