Rachel Reeves has accused Jeremy Hunt of “lashing out” at the Office for Budget Responsibility (OBR) as the watchdog prepares to publish a report on the Conservatives’ legacy.

Shadow chancellor Mr Hunt has written to the country’s top civil servant, claiming that the OBR risks “straying into political territory and failing to follow due process” over its handling of the review into this year’s spending plans.

The review was launched after Ms Reeves replaced Mr Hunt in 11 Downing Street following Labour’s election win and a Treasury audit unearthed what she claimed was a £22 billion “black hole” in the plans she inherited.

The OBR’s review will be published on Wednesday alongside the Budget forecasts.

Mr Hunt wrote to Cabinet Secretary Simon Case to complain that the report “will be used for highly political purposes” and has not been shown in advance to Tory former Treasury ministers.

He told Mr Case: “I am a strong supporter of the OBR and its role in enhancing the UK’s economic credibility.

“But I hope you would agree that straying into political territory and failing to follow due process like this demeans it and also is deeply problematic for perceptions of the impartiality of the Civil Service.”

Mr Hunt and Ms Reeves clashed over the issue at Treasury questions in the Commons.

The shadow chancellor said: “We all know why she’s inventing this fictitious black hole. Thirty times this year before the election she promised not to raise tax and tomorrow she’s planning the biggest tax-raising budget in history.”

Ms Reeves hit back: “I think it is important we don’t deny the seriousness of the situation that we face with the black hole in the public finances. Combined with lashing out at independent economic institutions, (it) suggests that he’s got more in common with Liz Truss or Kwasi Kwarteng than perhaps we thought.

“I watched my party lurch towards an ideological extreme and deny reality, and, as a result, we spent years in opposition. The shadow chancellor risks taking his party down the same path.”

Budget 2024
Chancellor Rachel Reeves hit out at Jeremy Hunt in the Commons (House of Commons/UK Parliament/PA)

Former prime minister Ms Truss and her chancellor Mr Kwarteng sidelined the OBR when announcing the ill-fated mini-budget measures in September 2022.

OBR chairman Richard Hughes said the watchdog’s review is “concerned with the adequacy of the information and assurances” it was given by Mr Hunt’s Treasury in the run-up to the March 2024 Budget.

Downing Street said Sir Keir Starmer will “back the independent OBR, not trash it”.

The Prime Minister’s official spokesman denied the body is being used as a political tool, adding: “The answer is not to blame the referee, face up to the challenges we face and be honest about the trade-offs and choices the Government face, not pretend they don’t exist.

“That’s why the Government is strengthening the OBR through the Budget Responsibility Act to ensure that it’s never sidelined again, like we saw during the mini-budget.

“The Government has been upfront about the black hole of the nation’s finances and it fully backs the OBR and the independent scrutiny it provides.”