Sir Keir Starmer has branded Rishi Sunak a liar and claimed he had broken the ministerial code for suggesting Labour planned to hike taxes by more than £2,000.
The Labour leader said the Prime Minister’s actions had given an “insight into his character”.
The comments came after it emerged senior officials had told ministers not to say civil servants were behind Tory claims that Sir Keir was planning tax hikes if elected.
The Prime Minister repeatedly highlighted the allegation during his ITV head-to-head debate with Sir Keir, claiming “independent Treasury officials” have costed Labour’s policies “and they amount to a £2,000 tax rise for everyone”.
But the Treasury’s permanent secretary, James Bowler, said ministers had been told not to suggest civil servants produced the figure at the heart of the Tory attack.
As the Prime Minister doubled down on the attack with an online advert, Sir Keir said: “What you saw last night was a Prime Minister with his back against the wall, desperately trying to defend 14 years of failure, resorting – and it was a flash of his character, an insight into his character – to lies. I don’t say that lightly.”
He told LBC: “He breached the ministerial code because he lied and he lied deliberately.
“Because we have made clear that our plans are fully costed, fully funded, they do not involve tax rises for working people – so that’s no income tax rise, no national insurance rise, no VAT rise.
“And the Prime Minister, with his back against the wall, desperately trying to defend his awful record in office, resorted to lies and he knew what he was doing, he knew very well what he was doing.”
The row stems from a document produced by the Conservatives which made a series of assumptions to estimate the cost that might be attached to potential Labour policies.
It stated that Labour’s plans had a £38.5 billion deficit over four years, the equivalent of £2,094 for every working household, which the Tories claim would be filled with tax hikes.
Some of the estimated costings in the document were produced by civil servants at the Treasury, using assumptions provided by politically appointed special advisers.
But Mr Bowler said the headline figure used by the Tories should not be attributed to impartial civil servants because it went beyond that official work.
In a letter to Labour’s shadow Treasury chief secretary Darren Jones, he said the £38.5 billion total for Labour policies in the Tory document “includes costs beyond those provided by the Civil Service”.
“Costings derived from other sources or produced by other organisations should not be presented as having been produced by the Civil Service,” he said in a letter to Mr Jones on June 3.
“I have reminded ministers and advisers that this should be the case.”
The Office for Statistics Regulation confirmed it was looking into the use of the £2,000 figure.
Energy Secretary Claire Coutinho repeated the claim on Wednesday, saying it was based on “official costings from the Treasury” and suggested it had been “signed off” by Mr Bowler.
She told BBC Breakfast: “I’ve worked in the Treasury and I can tell you that these are brilliant, independent civil servants and they would not be putting anything dodgy in there.”
On Times Radio, Ms Coutinho even claimed “this is something which has been signed off by the permanent secretary of the Treasury”, adding “those costings have been done by independent Treasury civil servants”.
And Mr Sunak said: “It couldn’t have been clearer in last night’s debate. Keir Starmer’s tax rises will cost working families £2,094.”
He posted a Tory attack video highlighting the figure.
Polls suggested neither Mr Sunak nor Sir Keir landed a knockout blow during the ITV clash on Tuesday night.
A snap poll from YouGov suggested the Prime Minister performed marginally better, with 51% making him the winner against 49% for Sir Keir among people who expressed a preference.
But a Savanta survey pointed to a more convincing victory for Sir Keir on 53%, ahead of Mr Sunak on 47%, excluding those who said they did not know.
Perhaps the most telling findings from the YouGov survey were that 62% found the ITV debate frustrating and just 17% found it a helpful exercise.
YouGov surveyed 1,657 British adults on Tuesday, and Savanta surveyed 1,153 people who watched the debate after it concluded.
Campaigning on Wednesday will be low key as commemorations for the 80th anniversary of D-Day begin.
Both Mr Sunak and Sir Keir attended the UK’s national commemoration event in Portsmouth alongside members of the royal family and armed forces veterans, before attention is focused across the Channel for further anniversary events in Normandy on Thursday.
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