Detectives investigating alleged Downing Street and Whitehall rule-breaking parties are to begin contacting more than 50 attendees this week.
The Metropolitan Police said it would be sending notices asking for “an account and explanation of the recipient’s participation in an event”, and added the inquiry has been named Operation Hillman.
The announcement on Wednesday came hours after the force said it is reviewing whether a Christmas quiz at No.10 may have breached Covid-19 restrictions after a picture emerged showing Boris Johnson and colleagues near an open bottle of champagne.
Officers will send formal questionnaires to more than 50 people, starting by the end of this week, in relation to eight dates that are being investigated between May 20 2020 and April 16 2021.
“This document, which asks for an account and explanation of the recipient’s participation in an event, has formal legal status and must be answered truthfully,” the Met said.
“Recipients are informed that responses are required within seven days. In most cases contact is being made via email.”
The statement added: “It should be noted that being contacted does not mean a fixed penalty notice will necessarily be issued to that person.
“Nevertheless, if following an investigation, officers believe it is appropriate because the Covid regulations have been breached without a reasonable excuse, a fixed penalty notice will normally be issued.
“We understand the interest in and impact of this case, and are progressing the investigation at pace. We are committed to completing our investigations proportionately, fairly and impartially.”
Sue Gray’s interim report last week disclosed that police were investigating 12 different events in No 10 and Whitehall over the course of 2020 and 2021 for possible breaches of Covid rules.
They include the notorious “bring your own booze” event in the Downing Street garden in May 2020 attended by Johnson and a gathering in the Prime Minister’s official flat in November 2020.
The Met said the Operation Hillman special inquiry team was continuing to examine more than 500 documents and 300 images provided to them by the Cabinet Office and would be seeking further information to assist their inquiry.
It warned that there may be a need to contact further people in the coming days and weeks should they be identified as having taken part in an event that potentially breached regulations.
Earlier The Mirror published a photo showing the prime minister and three members of staff – one wearing tinsel and another in a Santa hat – near what appears to be an uncorked bottle of prosecco and an open bag of crisps at the “virtual quiz” night on December 15 2020.
In a statement, the Met said it had previously been assessed that the event did not meet the “threshold for criminal investigation” but that decision was being reviewed.
At prime minister’s questions Johnson was challenged by Labour MP Fabian Hamilton, who said the image appeared to show “one of the Christmas parties he told us never happened”.
He added: “Will the prime minister be referring this party to the police as it is not one of the ones currently being investigated?”
Johnson responded: “In what he has just said, I’m afraid he is completely in error.”
Challenged again during PMQs, Johnson added: “That event already has been submitted for investigation.”
Dominic Cummings, Johnson’s hostile former chief adviser, tweeted “there’s waaaaay better pics than that floating around”, including of inside Johnson’s official Downing Street flat.
Adam Wagner, a human rights lawyer who has been examining Covid laws, said it “seems obvious” from the new photo that Johnson is “participating in a social gathering”.
The prime minister’s press secretary insisted the event was a “virtual quiz” but was unable to say whether the photograph had been submitted to the Gray inquiry.
“I’m not going to get into precise evidence but she obviously had access to all the evidence she needed,” the press secretary said.