British Prime Minister Boris Johnson is expected to be among 50 people in Downing Street who will be questioned by police as part of an investigation into lockdown-breaching parties.
Scotland Yard said by the end of the week officers will have started sending out formal legal questionnaires to more than 50 individuals.
The events under investigation include a number known to have been attended by Mr Johnson, raising the prospect that he will be among those receiving a demand for answers in their inboxes.
The force said it would give each individual seven days to respond to the questionnaire which in most cases is being sent by email.
Questions will include whether they attended one or more parties on the following dates:
- May 20, 2020
- June 18, 2020
- June 19, 2020
- November 13, 2020
- December 17, 2020
- December 18, 2020
- January 14, 2021
- April 16, 2021
The Met said detectives were examining more than 500 documents and 300 photos provided by the Cabinet Office and further information would be sought.
On Thursday a new photo emerged showing the prime minister in a room with an open bottle of wine. He could be seen with three members of staff, one wearing tinsel and another in a Santa hat, near a bottle of bubbly and an open bag of crisps.
After the new evidence emerged, the Metropolitan Police said on Wednesday its officers were reconsidering their previous assessment that the event on December 15, 2020, did not meet the threshold for criminal investigation.
The new photo was published as Mr Johnson completed a Cabinet reshuffle designed to be a reset on his leadership, sparked by the Sue Gray investigation into "partygate" allegations of events that breached lockdowns.
"[We] previously assessed this event and determined that on the basis of the evidence available at that time, it did not meet the threshold for criminal investigation,” the Metropolitan Police said.
"That assessment is now being reviewed."
Detectives investigating the lockdown parties will send out questionnaires to people believed to have taken part, Scotland Yard said.
Officers from Operation Hillman will begin contacting more than 50 people thought to have been involved.
The claims centre on events and gatherings in government buildings while the rest of the country was living under strict lockdown rules, unable to socialise or visit family members in hospital.
Downing Street insisted the December 15 event was a "virtual quiz" and that police had decided not to investigate it along with 12 other events after receiving evidence from the Gray inquiry.
The police review suggests the latest image to surface was not among more than 300 passed to officers by the Whitehall investigation.
Even before police said it was reviewing its decision, Mr Johnson was under pressure from some of his own MPs to resign.
A major Conservative Party donor, John Armitage, also called on the prime minister to resign, saying his premiership is “past the point of no return”.
Conservative MP Neil Hudson called for all the evidence to be published to stem the "drip, drip, drip" of alleged Covid breaches and "upsetting images".
"I'm incredibly disappointed and upset. Yet again I have to say that categorically I will not defend the indefensible," Mr Hudson said.
"I'm very clear that if rules have been broken, and indeed if the law has been broken, it doesn't matter how serious you are, there has to be serious consequences."
Dominic Cummings, Mr Johnson's hostile former chief adviser, tweeted: "There's waaaaay better pics than that floating around", including some inside Mr Johnson's official Downing Street flat.
London was under Tier 2 restrictions at the time, which prohibited indoors social mixing between different households.
"Although there are exemptions for work purposes, you must not have a work Christmas lunch or party, where that is a primarily social activity and is not otherwise permitted by the rules in your tier," official guidance said.
