Dame Meg Hillier has written to HM Treasury and the Financial Conduct Authority about a potential leak of market-sensitive information before Wednesday's Budget.
The Treasury Committee said a Bloomberg report published at 10.45am contained accurate information about bank-tax announcements made later that day by Chancellor John Healey.
The report was updated at 11.03am to note movements in bank share prices. The committee said the story appeared to have affected those prices.
Hillier's letters, dated 28 October and published by the committee on Thursday, ask the Treasury and the financial regulator to address the Budget security and market-sensitivity issues raised by the episode.
The letters are separate from Hillier's welcome for the Budget decision to keep the £20,000 cash ISA limit. They concern the handling of information before the fiscal statement rather than the policy announced in it.
Hillier is the Labour and Co-operative MP for Hackney South and Shoreditch and has chaired the Treasury Committee since September 2024.
