The prime minister’s office, No 10 Downing Street, had previously claimed Johnson had not been aware of any “specific allegations”, after Pincher’s dramatic resignation last week as deputy chief whip following claims he groped two men at a private members’ club.

“At the time last week that was the prime minister’s view. You will appreciate it takes some time to establish he was briefed, albeit we don’t think in formal briefing on this,” the spokesman said.

“This dates back a number of years. On Friday, it was our belief that he was not informed about that specific incident.”

The admission came after the former top civil servant at the Foreign Office, Lord Simon McDonald, said the original No 10 account was “not true” and the prime minister had been briefed “in person”.

In the House of Commons, responding to a Labour urgent question, Cabinet Office minister Michael Ellis told MPs: “The prime minister was made aware of this issue in late 2019, he was told that the permanent secretary had taken the necessary action, no issue therefore arose about [Mr Pincher] remaining as a minister.

UK lawmaker who ‘drank far too much’ quits government amid groping reports

“Last week, when fresh allegations arose, the prime minister did not immediately recall the conversation in late 2019 about this incident. As soon as he was reminded, the No 10 press office corrected their public lines.”

For Labour, deputy leader Angela Rayner said the latest disclosures revealed an “ethical vacuum” at the heart of Downing Street.

“The prime minister was personally informed about these allegations and yet he was either negligent or complicit,” she said.

William Wragg, the Conservative MP who chairs the Commons Public Administration and Constitutional Affairs Committee, said ministers should consider how long they were prepared to carry on supporting the government.

“I would ask them to consider the common sense of decency that I know the vast, vast majority of them have and ask themselves if they can any longer tolerate being part of a government which, for better or worse, is widely regarded of having lost its sense of direction,” he told the House.

Since Pincher’s resignation on Thursday, Johnson has been under pressure to say what he knew about his conduct when in February he made him Tory deputy chief whip – a position in which he has responsibility for MPs’ welfare as well as discipline.

Over the weekend a series of reports emerged of allegations over a period of years that Pincher repeatedly made unwanted sexual advances to men.

On Monday, Johnson’s spokesman amended the government’s line to say that while the prime minister had been aware of media reports and speculation, any issues had been resolved and they had not led to formal complaints.

Keep your hands in your pockets, British minister tells male MPs

But McDonald said the position was still “not accurate”. In a letter to the parliamentary standards commissioner he said that a group of officials had complained to him about Pincher’s conduct along similar lines to his alleged behaviour at the Carlton Club.

Following an investigation, the complaint was upheld, Pincher apologised and promised there would be no repeat of his behaviour.

“Mr Johnson was briefed in person about the initiation and outcome of the investigation,” McDonald wrote.

“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.”