The prime minister’s office said he had been given the legal form by the Metropolitan Police yesterday. A Downing Street spokesperson said the PM “will respond as required”.
It means Mr Johnson will have to provide a credible reason to explain why he was at events held during Covid restrictions, or face a fine.
Meanwhile there is mounting pressure on the PM to resign after another senior Conservative weighed in on the Partygate scandal.
Ex-Tory leader Iain Duncan Smith said it would be difficult for Mr Johnson to stay on if the Met probe concludes he broke Covid rules and issues a fine.
“I think it would be very tough for anyone to remain after that,” he told the i newspaper.