The new floor under UK bank capital
Basel 3.1 represents the most significant overhaul of the UK bank capital framework since the original implementation of Basel III in 2014. The Prudential Regulation Authority's near-final rules, published across two policy statements, will take effect from 1 January 2027 - giving institutions a compressed window to translate technical policy into operational change across credit risk, market risk, operational risk and the output floor.
For UK firms, the headline change is the introduction of a 72.5% output floor on internally-modelled risk-weighted assets, phased in through to 2030. The PRA has chosen a single-stack approach, applying the floor at the consolidated level - a design choice with material implications for portfolio composition, pricing and the long-run viability of internal model approaches in some asset classes.
What's changing in credit risk
The standardised approach for credit risk has been comprehensively rebuilt. Risk weights for unrated corporate exposures, real estate (both residential and commercial), and specialised lending have all been revised - in some cases materially. Banks that have historically run a hybrid IRB/SA portfolio will need to re-run portfolio analysis to understand the post-3.1 economics of each business line.
For internally-modelled approaches, the changes are even more substantive. Foundation IRB becomes the only modelling option for large corporate exposures, sovereign exposures shift to the standardised approach, and a new set of input floors will constrain PD and LGD estimates for retail mortgages and other key asset classes. The combination of input floors and the output floor is what will drive the binding constraint for many UK banks - and the answer to which is binding will vary materially by business mix.
Operational risk: a single standardised approach
The advanced measurement approach for operational risk is being retired entirely. All firms will move to a single standardised approach based on the Business Indicator Component, with a multiplier driven by historical operational losses. The change is broadly capital-neutral at the system level, but firms with low historical loss experience and a heavy modelled allocation will see meaningful capital uplift, while others will benefit. Either way, the data, governance and reporting requirements around the BIC and the Internal Loss Multiplier are non-trivial.
We see firms underestimating the data quality and lineage workstream required to support the new operational risk framework - particularly around the ten-year loss data history. Beginning that work now is far cheaper than retrofitting it under regulatory scrutiny in 2026.
What banks should be doing now
By the start of 2026, leading institutions will have completed parallel runs on the new framework, identified the binding constraint at portfolio and entity level, and begun pricing the implications into front-office decisions and capital plans. They will have also concluded the strategic review of which business lines remain economic under the new framework, and which require pricing or model changes to remain so.
The compressed timeline means that change programmes spanning credit policy, model development and validation, finance system change, regulatory reporting and management information cannot run sequentially. The firms that will be ready in 2027 are the firms running these workstreams in parallel today, with senior accountability and a clear view of the operational target state.