Shadow Chancellor Mel Stride has warned that the Budget leak "could be a criminal offence" as he demanded an inquiry into the OBR.
He spoke in the Commons ahead of Rachel Reeves delivering her Budget to the House.
An "unprecedented" leak has seen key measures from the Budget accidentally published way ahead of schedule.
Mel Stride said: "We have seen an unprecedented leak of the OBR Economic and Fiscal Outlook report before the Budget.
"This report contains market sensitive information.
"It is utterly outrageous that this has happened, and this leak may indeed constitute a criminal act."
"In Prime Minister's Questions, the Leader of the Opposition asked the Prime Minister about this leak, but he refused to answer her question.
"So, Madam Deputy Speaker, please can you advise this House what steps are at its disposal to force a leak inquiry into this matter?
Mel Stride demanded an inquiry into the leaks
|GB NEWS
"Would it be possible to ask them to distribute copies of the report to the House, given that everybody outside of this House has already had the opportunity to read it?"
The leaked OBR report revealed that the Chancellor will freeze tax thresholds until 2030, raking in £8billion for the Treasury.
It also shows debt is on course to hit 69 per cent of GDP by the end of the decade.
Markets reacted immediately, with gilt yields tumbling amid growing fury over the leak.
In a blow to Rachel Reeves, projected growth has been downgraded every year from 2026 with GDP expected to hit just 1.5 per cent in 2025 and 1.9 per cent in 2026.
Fuel duty will stay on hold until September 2026, while the two-child cap on Universal Credit is due to be lifted from next April, a change expected to cost £5.3 billion before the next election.
But the leaked OBR report warns Reeves is lining up £26 billion in tax increases.
If delivered, the UK’s tax burden would climb to an unprecedented 28 per cent of GDP by 2031.
Kemi Badenoch asked a similar question before the Chancellor
|GB NEWS
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That would hand Ms Reeves around £22billion in fiscal headroom boosted by a raid on pension contributions worth £4.7billion.
A proposed pay-per-mile charge on electric vehicles is forecast to bring in £1.4billion, with higher gambling duties adding another £1.1billion.
The apologised for publishing their analysis of the Budget "too early", blaming it on a "technical error" and said they have initiated an investigation into how this happened.
They added: "We will be reporting to our Oversight Board, the Treasury, and the Commons Treasury Committee on how this happened, and we will make sure this does not happen again."
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