The Treasury committee has launched a probe into a potential Budget leak that sent shares in Britain’s banking giants soaring.

The group of influential MPs have said a leak inquiry is underway after news of John Healey’s decision to double the UK banking surcharge emerged in the press hours before the Chancellor delivered his Budget.

It follows Treasury Permanent Secretary James Bowler writing to the chair of the Treasury committee, Dame Meg Hillier, confirming an investigation led by the Government Security Group was underway.

“I have been assured that no banks, their representatives or their trade bodies were briefed by Treasury on the details of the changes to the bank corporation tax surcharge before the publication of the Budget and the Chancellor’s statement to the House,” Bowler said.

But he added in there is a “necessary widening of the circle of knowledge within the government” ahead of the delivery of the Budget.

Healey hiked the banking surcharge to six per cent for 15 months in his Budget. Bloomberg reported hours before the speech that the tax would be raised below the eight per cent originally expected and be temporary.

Treasury committee chair sounds off on ‘doom-loop’ inquires

Shares in Lloyds, Natwest and Barclays all popped following the reports as the sector celebrated a softer-than-feared tax increase.

“I suspect that yet another inquiry into the leak of Budget measures will turn up no evidence of a breach but plenty of reassurance that next time it will be even more secure. And so the cycle continues,” chair of the Treasury committee, Dame Meg Hillier, said.

“We cannot continue to accept this doom-loop of dead-end investigations in which everybody in the Treasury throws their hands up in despair, but nobody is ever found to have done anything wrong.”

Healey will take questions from the Treasury committee tomorrow as part of a post-Budget routine. Hillier said she would be “pushing for answers” as part of the hearing.

Financial Conduct Authority chief Nikhil Rathi has also vowed to engage with government officials regarding a potential leak, and whether “any unlawful disclosure of inside information may have occurred”.

In a letter to Hillier, the boss of the City’s top regulator said the watchdog may “choose to intervene where that discourse, or poor information handling, impacts markets improperly”.

“We stand ready to consider the specifics of any evidence provided to us by Cabinet Office and HMT to decide what, if any, action it is appropriate for us to take,” he said.