Last month Sue Gray, a senior civil servant, published a 12-page “update” into the claims that revealed a gathering in the Prime Minister’s own Downing Street flat was one of a dozen events being investigated.

The civil servant said there had been a “failure of leadership”, warned against “excessive” drinking from government officials inside No 10 and declared that some of the events should never have taken place.

Scotland Yard is currently investigating 12 alleged gatherings across eight separate dates between May 20 2020 and April 16 2021.

Detectives begin interviewing key witnesses

This week detectives began interviewing key witnesses in the “partygate” investigation, after some of those accused of breaking lockdown rules refused to accept fines.

Recipients of the legal binding documents are given seven days in which to respond and accept their guilt or offer a “reasonable excuse” for their alleged actions.

Scotland Yard said that while no fines had yet been recommended, detectives had started to interview key people as witnesses, suggesting at least some of those accused had indicated they wished to fight their case.

Boris Johnson received and returned a questionnaire to police last month, but a Downing Street source said he had not yet been interviewed.

Carrie Johnson, the Prime Minister’s wife, who helped organise a surprise birthday party for him, is also among those thought likely to have received a questionnaire.

Last month it was confirmed that Rishi Sunak, the Chancellor, had also received a questionnaire and would have to account for his presence at Mr Johnson’s birthday event.