Britain’s banks have spent years planning for Basel 3.1. What they are now planning around is Britain’s version of it: a regime that keeps the international headline date but quietly moves the pieces that matter most to a trading desk, and hints at more divergence to come.
The core of Basel 3.1, the last tranche of the post-2008 capital rulebook, takes effect in the UK on 1 January 2027. The Prudential Regulation Authority nailed that down in its final rules, PS1/26, published on 20 January. It is already a year later than first planned: the PRA, with the Treasury, pushed the start from 2026 to 2027 back in January 2025, tracking the timetable of a United States that has yet to commit to its own version at all.
The more revealing move came in June. In CP9/26, published on 19 June, the PRA proposed to hold back the part of Basel 3.1 that bites hardest on investment banks (the internal model approach, or IMA, for market risk) by a further year, to 1 January 2028. In the interim, from January 2027, firms keep their existing model permissions. For the year the core regime is live, in other words, the banks with the largest trading books will still be running the old market-risk machinery.
That is not a drafting quirk. The IMA lets a bank use its own models, rather than a regulator’s standardised formula, to size the capital it holds against trading losses, and the gap between the two can run to billions. Delaying it to 2028 buys the PRA time to coordinate with other jurisdictions, most of which use the same models across cross-border desks, and spares UK-based trading operations a unilateral capital hit while Washington dithers.
The consultation goes beyond timing. Its centrepiece is the profit-and-loss attribution test: the pass/fail gate that decides whether a desk may keep using its own models at all. The PRA proposes to stretch the monitoring period for that test from one year to three, and to keep it non-binding throughout, giving itself time to gather data and confirm the calibration before capital consequences attach. It is a regulator explicitly declining to flip a hard switch it is not yet sure is set correctly. The consultation closes on 18 September.
Read together, the two moves describe a UK that has stopped treating Basel as a deadline to be met and started treating it as a framework to be calibrated. The direction is set out plainly elsewhere. In late April, the PRA’s executive director for prudential policy, David Bailey, laid out a road map for the UK banking framework spanning capital, liquidity, ring-fencing, mortgage lending, securitisation and reporting, the clearest signal yet that 2027 is a waypoint, not a terminus.
The competitiveness thread runs through all of it. The PRA has framed Basel 3.1 as broadly capital-neutral for large UK firms, and expects an aggregate benchmark of around 13% common equity to be reflected from 2027: not a step up in the total the system holds, but a redistribution of where it sits. The aim is to comply with the global standard without handing London a cost that New York, and on a different timetable Frankfurt, do not carry.
Ring-fencing is the other front. Alongside the Treasury’s May review, Safeguarding Stability, Enabling Growth, the PRA has signalled reforms to how ring-fenced banks share operational services, with a consultation due this summer, and has said the Financial Policy Committee will examine how ring-fencing interacts with two of Basel 3.1’s own levers: the output floor and the leverage ratio. That is capital policy and structural policy being tuned in the same breath, both pointed at the objective the government keeps repeating: growth, without unpicking the stability architecture built after the last crisis.
For UK bank treasurers and their boards, the practical message is that the 2027 capital plan is now a moving target with a firm floor. The core regime is fixed for January 2027 and worth building to. The market-risk models (the piece that most shapes an investment bank’s capital intensity) are provisionally a 2028 problem, on rules still out for consultation. And the wider calibration, from the output floor to ring-fencing perimeters, is openly under review.
The risk in a self-calibrated path is the mirror of its appeal. Divergence that eases the burden today can fragment tomorrow: a UK-specific rulebook is one more variant for cross-border groups to model, and one the PRA must defend as prudent rather than merely accommodating. For now, the regulator’s bet is that it can hold Basel’s substance while setting Britain’s own clock. 2027 will show whether the market reads that as confidence or as drift.
Sources: Bank of England / PRA: PS1/26 “Implementation of Basel 3.1: Final rules”; CP9/26 “Basel 3.1: Adjustments to the internal model approach (IMA) for market risk”; PRA news, “PRA sets out adjustments to its market risk internal model approach under Basel 3.1” (Jun 2026); PRA road map for the future UK banking prudential framework (Apr-May 2026); HM Treasury, “Safeguarding Stability, Enabling Growth: The Ring-Fencing Review” (May 2026).
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