Caps on mortgage borrowing have been imposed in the UK, with the Bank of England extending an activist program sparked by the GFC.Banks in the UK must now ensure they do not extend more than 15 per cent of the total number of their new residential mortgages at loan to income multiples at or greater than 4.5 times. The measure was made "with the intention of capturing macroprudential risks associated with excessive household indebtedness," the BOE said last week.For Australian banks the policy choice is of interest, with the Financial System Inquiry panel finalising their report and aiming to guide policy choice at home.The BOE's stance may serve as a reminder that any optimism around watering down Basel 3 will have to be tempered.Most of these choices will be made by APRA, under the returned leadership of Wayne Byres, a central figure in international banking regulation. Byres is completing a term as secretary of the Basel Committee on Banking Supervision.Byres must be assumed to be an enthusiast for most details of the present banking reform agenda and an interested associate of BOE governor Mark Carney.Carney remains chairman of the G20's Financial Stability Board.It is unlikely either Carney nor Byres will care to be drawn into accommodating any parochial agendas at Brisbane's G20 gathering in September.