John Healey is facing pressure to clarify whether he permitted a market-sensitive budget leak before his statement, which moved bank share prices.

The chair of the influential Commons Treasury select committe, Meg Hillier, has written to the Treasury and the Financial Conduct Authority watchdog (FCA) to assess whether a story leaked to Bloomberg, and published more than an hour before the budget was revealed, led to an “improper release of inside information”.

Shortly before Healey left Downing Street to deliver his budget statement in the Commons at 12.30pm, the prices of shares in banks moved as Bloomberg had published a story at 10.45am noting the bank corporation tax surcharge would be lower than the 8% that lenders had feared, and the increase would only be temporary.

In a letter to James Bowler, the permanent secretary of the Treasury, and the chief executive of the FCA, Hillier wrote: “There were two elements to the Bloomberg story, namely that the bank surcharge would not reach 8% and that it would be temporary.

“HM Treasury’s Budget 2026 confirmed the following: ‘Bank Surcharge: Temporarily increase the Bank Corporation Tax Surcharge rate from 3% to 6%, to fund breathing space measures for households, for 15 months from 1 January 2027’. The Bloomberg story quoted ‘people familiar with the matter’.

“This appears to have been more than idle speculation, and it had implications for relevant securities.”

Writing directly to the FCA, Hillier noted the body’s responsibility for “market cleanliness” and its implementation of “the UK’s market abuse regulation”, adding, “I would welcome your view on whether this event might be considered an improper release of inside information and your assessment of its impact on the market in relevant securities.”

Separately, she urged Bowler to confirm “that banks (or any representatives of them or their trade bodies) were not told of the changes in outline or with specifics before” the budget and “how many people had access to the information” related to the bank surcharge changes.

Healey confirmed the surcharge would rise from 3% to 6% for 15 months from 1 January 2027 as he told MPs in the Commons: “I am looking to our banks to help fund breathing space for British families. And so banks will pay an extra 3% on the bank surcharge. This will be time-limited to pay for immediate support on energy bills, starting in January, ending 15 months later.”

Commons sources are concerned that bankers were able to make money out of the measures that were leaked to Bloomberg an hour and a half before the measures were confirmed.

The chancellor will be asked to explain this leak when he appears before the Commons Treasury select committee next month. But in the meantime, Hillier has urged the Treasury and the FCA to investigate what happened and to confirm that “banks were not told of the changes in outline or with specifics before the publication of the budget”.