Since the deputy chief whip resigned his post last week after allegations of groping two men, Number 10 has said the prime minister was not aware of specific allegations.

But Lord McDonald, who was the permanent secretary in the Foreign Office between 2015 and 2020, has written to parliament's standards commissioner saying Downing Street had made "inaccurate claims".

Politics Hub: Boris Johnson under mounting pressure for explanation

Tweeting the letter, he said: "This morning I have written to the Parliamentary Commissioner for Standards - because No 10 keep changing their story and are still not telling the truth."

In the letter, he wrote: "The original No 10 line is not true and the modification is still not accurate. Mr Johnson was
briefed in person about the initiation and outcome of the investigation.

"There was a 'formal complaint'. Allegations were 'resolved' only in the sense that the investigation was completed; Mr Pincher was not exonerated. To characterise the allegations as 'unsubstantiated' is therefore wrong."

Mr Johnson led a cabinet meeting this morning, letting cameras in for his opening remarks - but not allowing any questions from journalists.

Surrounded by his serious-faced ministers, the PM spoke about the cost of living crisis and his plans to tackle it, but there was no mention of Mr Pincher or Lord McDonald's letter.

Tory MP and critic of the PM John Penrose called the letter "dynamite", tweeting it showed "another serious breach" of the ministerial code and that Mr Johnson's "promised reset" after Partygate had "no credibility because their behaviour hasn't changed at all".

Shortly before the letter was published, Deputy Prime Minister Dominic Raab told Sky News' Kay Burley that he knew about the allegation when he was foreign secretary in 2019.

He said he had "made it clear in no uncertain terms" to Mr Pincher that the behaviour "must never be repeated", and he referred it to both the civil service and Cabinet Office for investigation.

But Mr Raab said the inquiries did not "trigger disciplinary action", and he had only told the PM about the incident "in recent days".

The deputy PM also described Mr Pincher as "an exceptional minister" and said it was right to allow the independent investigation to make its own conclusions.

Labour's deputy leader Angela Rayner said it was "now clear that the prime minister knew about the seriousness of these complaints but decided to promote this man to a senior position in government anyway", adding: "He refused to act and then lied about what he knew.

"Boris Johnson is dragging British democracy through the muck. His appalling judgement has made Westminster a less safe place to work."

Mr Pincher resigned as the government's deputy chief whip on Thursday after allegations he drunkenly groped two men at a private members club in London earlier that week.

The party whip was only removed from him - leaving him sitting as an independent MP for his Tamworth constituency - on Friday afternoon after the PM bowed to pressure, and a formal complaint was made to parliament's Independent Complaints and Grievance Scheme (ICGS).

A number of ministers have since taken to the airwaves to reiterate Number 10's defence of Mr Johnson, including education minister Will Quince, who said he had been given "categorical assurance" the PM was not aware of any serious specific allegations.

But on Monday, Sky News revealed the PM's wife, Carrie Johnson, also questioned Mr Pincher's suitability as a government whip as far back as 2017.

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Labour's shadow attorney general, Emily Thornberry, said Downing Street "tells us different things on different days... and as time goes on, the truth starts to come out".

She told Sky News that Mr Johnson had been "turning a blind eye to any allegations because it suited the prime minister to turn a blind eye to it", adding: "We need a country that is led by a decent, honourable person."

The deputy leader of the Liberal Democrats, Daisy Cooper, also said Lord McDonald had "shone a new light on this murky cover-up".

She added: "Boris Johnson needs to own up to his web of lies and finally come clean today. Every day this carries on our politics gets dragged further through the mud."

And the SNP's Brendan O'Hara called for an investigation into the PM, saying the letter "demolishes Boris Johnson's claims and raises serious questions over whether he has lied and broken the ministerial code".