Rachel Reeves is expected to unveil a black hole in the public finances of around £20 billion, signalling that tax rises could be on the way.

The Chancellor will on Monday set out the results of the spending audit she ordered Treasury officials to produce.

Her update will reveal “the true scale of the damage the Conservatives have done to the public finances”, a Labour source said.

They did not deny reports that an early assessment has found a nearly £20 billion annual gap between revenues and funding commitments, including in areas such as asylum and public sector pay.

The figure could still shift as each department’s spending commitments are assessed before her Commons statement.

Any tax hikes to plug the shortfall in spending for essential public services are not expected before the autumn budget, the date of which Ms Reeves is also set to announce on Monday.

Labour has ruled out lifting income tax, VAT, national insurance and corporation tax, but changes to capital gains or inheritance levies may be on the table.

Asked about the black hole at a meeting of G20 finance ministers in Brazil, Ms Reeves said: “I’ll give a statement to Parliament on Monday, but I have always been honest about the scale of the challenge we face as an incoming Government, and let me be crystal clear: we will fix the mess we have inherited.”

Prime Minister’s Questions
Prime Minister Sir Keir Starmer has highlighted the dire state of the public finances (Lucy North/PA)

The Labour source said: “On Monday, the British public are finally going to see the true scale of the damage the Conservatives have done to the public finances.

“They spent taxpayers’ money like no tomorrow because they knew someone else would have to pick up the bill.

“It now falls to Labour to fix the foundations of our economy and that work has already begun.”

As she presents the findings of the audit, Ms Reeves is expected to confirm the plans of her Tory predecessor Jeremy Hunt would require significant cuts to already cash-strapped public services.

The Chancellor is widely expected to be forced to raise taxes in the budget to avoid the spending squeeze implied by the existing plans and to meet her fiscal rule to have debt falling as a share of gross domestic product in five years’ time.

Ms Reeves will also respond to the public sector pay recommendations as the Government faces having to find money for above-inflation rises.

Reports have suggested teachers and NHS workers could be in line for a 5.5% pay boost, which could cost about £3.5 billion more than had been budgeted.