A minister has dismissed calls for a probe into allegations that a second gathering took place in Downing Street on Boris Johnson's birthday.
Labour is demanding inquiries into leaked messages suggesting the Prime Minister's wife Carrie hosted several friends in the No11 flat on 19 June 2020.
Mr Johnson, his wife and Chancellor Rishi Sunak were all fined by police over a surprise birthday event for Mr Johnson in the Downing Street Cabinet room on 19 June 2020.
But the Sunday Times reported that civil service boss Simon Case had been informed of messages suggesting Mrs Johnson held another gathering in the No11 flat on that date.
Indoor socialising was banned under Covid rules at the time.
But Technology Minister Chris Philp said the Partygate saga was probably the "most thoroughly investigated set of incidents in recent times" and said "it is not immediately obvious" more inquiries were needed.
The event, which has not been denied, did not feature in Sue Gray's bombshell report into lockdown-busting parties in Downing Street published last week.
Mrs Johnson's spokeswoman said Ms Gray's team were aware of the exchanges as part of their "exhaustive" Partygate investigation.
Labour wrote to civil service boss Simon Case last night asking him to release correspondence relating to Mr Johnson's "whereabouts" that evening.
Angela Rayner said: "It is crucial that you now advise the Prime Minister to come clean about his involvement in this apparently rule-breaking gathering."
Mr Philp was asked if the alleged gathering should be investigated as questions mounted.
He said: "Well, I think we have had an unbelievably comprehensive set of investigations going on now for a period of nearly six months.
"We have had obviously the Sue Gray investigation published last week and she interviewed, goodness knows, dozens or possibly even hundreds of people in the course of her investigation, looked at emails, messages, and everything else.
"And we have had the Metropolitan Police investigation, which again, has gone over and gone on over a number of months. And they conducted that with full police powers.
"So, having had two separate investigations, including by the police over many months, it is not immediately obvious to me that we need any more investigations when this has probably been the most... rightly been, the most thoroughly investigated set of incidents in recent times."
Officials rejected the suggestion that Ms Gray had declined to look into claims of a second event on the night of Mr Johnson's 56th birthday.
An unnamed aide claimed to have told the investigation in January that they had messages showing Mrs Johnson met with "several" male friends that evening, with the Prime Minister later heading up to the flat where they were gathered.
The aide, who has since reportedly written to the Cabinet Secretary about the messages, told Ms Gray's team they did not want to forward the messages to them but were prepared to show investigators in person.
But the Cabinet Office said the informant had not been willing to provide the messages or to meet in person, so their email exchange was forwarded to the police once the Operation Hillman inquiry started.
The police did not investigate the alleged evening flat gathering and by the time the aide offered to share the messages with Ms Gray, the Cabinet Office said the probe had been wrapped-up.
Carrie Johnson's spokeswoman declined to tell the Mirror the purpose of the alleged flat gathering on 19 June 2020.
But she said: "As the Sunday Times acknowledges, Sue Gray was aware of these exchanges as part of her exhaustive inquiry into alleged breaches.
"Staff were given ample opportunity to present evidence including these messages and all relevant information was passed to the Metropolitan Police for investigation.
"The lunchtime gathering in the Cabinet Room on 19 June 2020 was subsequently found to be in breach and a fixed penalty notice was issued to Mrs Johnson among others for which she apologised unreservedly and promptly paid the fine.”
