Simon Hoare, a Conservative MP, suggested the gathering had been held to mark the return of Mr Johnson after his illness with Covid and to thank Mr Raab for standing in for him. But a spokesman for Mr Raab, the Justice Secretary, said that was “categorically untrue” and he had not attended the event.

Asked whether he had attended, Mr Gove, the Levelling Up Secretary, said he had been giving a statement to the Commons about the Northern Ireland Protocol, which finished at 2pm. His spokesman later said he had not attended.

A spokesman for Mr Sunak, who was absent from the Tory front bench on Wednesday as he visited a constituency in Devon, said he had not gone to the gathering despite it taking place in his own garden.

It is understood that, during the first Covid lockdown in early 2020, few Downing Street staff worked from the office except those crucial to the Government’s Covid response.

On Wednesday night, it was alleged that two of Carrie Johnson’s friends, Josh Grimstone and Henry Newman, also attended the party. Both were special advisers to Mr Gove. Neither of the men, nor Mr Johnson’s press secretary, responded to a request for comment about their attendance.

Questions were raised on Wednesday about Mr Johnson’s on defence for attending the gathering, with Dominic Cummings, his former chief adviser, tweeting that he knew it was “social not work” and was “no way ‘technically within rules'”.