A minister has said it is “not immediately obvious” an investigation is needed into allegations that Carrie Johnson held a lockdown party that was not part of the Sue Gray inquiry.

Chris Philp, the technology and digital economy minister, told Sky News’ Kay Burley that there has been an “unbelievably comprehensive set of investigations” over the past six months into parties that breached COVID regulations.

He said: “Having had two separate investigations, including by the police, over many months it’s not immediately obvious to me that we need any more investigations when this has probably, rightly, been the most thoroughly investigated set of incidents in recent times.”

Over the weekend The Sunday Times revealed that Cabinet Secretary Simon Case was told of previously unseen messages suggesting the prime minister’s wife held a gathering in the No 10 flat with several friends for her husband’s 56th birthday on 19 June 2020.

The prime minister is understood to have also been in the flat. At the time two or more people were banned from being indoors except for work purposes.

The event has not previously been made public and is understood to have not been part of the Sue Gray investigation.

Messages flagged up to Mr Case allegedly show a Downing Street aide told Mrs Johnson her husband was on the way up to the flat, with her replying she was already there with some male friends.

Mrs Gray was informed of the messages in January by the aide but they did not want to forward the messages but said they would show them to inquiry officials in person. They agreed to supply them to the Met Police’s inquiry.

The aide claims the Gray investigation team failed to follow up on the offer and once the Met’s investigation concluded two weeks ago, the aide offered the messages to the Gray team but nothing happened.

But the Cabinet Office said the aide did not offer to bring the messages in to them and despite being asked to provide all relevant information to the Gray inquiry, they did not.

Ms Gray’s team did provide the email exchange with the aide on the issue to Met detectives, the Cabinet Office said.

They added that the aide only offered to share the texts when they were just about to publish the Sue Gray investigation last week but did take into account the aide’s comments made after the Met report concluded that they were asked to organise the flat party.