Twenty fines will be issued as part of the police inquiry into Downing Street parties that broke Covid rules.
The Met police will not be saying who is fined or which events the fixed penalty notices relate to.
However, Downing Street has said before that it would confirm if the prime minister was facing a fine.
Fixed penalty notices are a sanction for breaking the law, and mean a fine, which needs to be paid within 28 days, or contested.
If someone chooses to contest the fine, the police will then review the case and decide whether to withdraw the fine or take the matter to court.
The police said they were attempting to progress the investigation, with a "significant amount" of material still to be assessed and that more fines could come in the future.
The police have been investigating 12 events that may have breached coronavirus lockdown rules, including at least three attended by Boris Johnson.
As part of their inquiries, they have sent out over 100 questionnaires to ask about people's participation in the events.
Reports of gatherings in Downing Street and Whitehall during the lockdown prompted public anger and several Conservative MPs called for the prime minister to resign.
However, since the outbreak of the war in Ukraine, some have withdrawn their demand.
Others have said they are withholding judgement until the police conclude their investigation, and an internal inquiry is published.
Johnson had previously insisted that "guidelines were followed at all times".
He later apologised for attending a drinks party in the Downing Street garden in May 2020, but insisted that he believed it was a work event.
A No 10 spokesman said he did not believe Johnson had misled the House of Commons, adding: "You will hear from the prime minister at the conclusion of the Met's investigation."
He added: "The PM's apology for how this was handled is a matter of record."
The spokesman also said Johnson had not received a fine.
If either the prime minister or Simon Case - the country's most senior civil servant - got a fine, it would be made public, No 10 said.
Labour's deputy leader Angela Rayner said: "After over two months of police time, 12 parties investigated and over a hundred people questioned under caution, Boris Johnson's Downing Street has been found guilty of breaking the law.
"The culture is set from the very top. The buck stops with the prime minister, who spent months lying to the British public, which is why he's got to go."
Sir Ed Davey, leader of the Liberal Democrats, said "If Boris Johnson thinks he can get away with partygate by paying expensive lawyers and throwing junior staff to the wolves, he is wrong.
"We all know who is responsible. The prime minister must resign, or Conservative MPs must sack him."
A campaign group for bereaved relatives of people who died with Covid said the prime minister "should have resigned months ago over this".
In a statement, the group said: "It's crystal clear now that whilst the British public rose to the challenge of making enormous sacrifices to protect their loved ones and their communities, those at 10 Downing Street failed."
However, former health secretary Matt Hancock defended Johnson had got "the big calls" right and was was "the best person to lead the country".
He added that he would stand by the prime minister even if he was fined by the police.
When stories emerged about events held in government buildings during the Covid lockdowns, senior civil servant Sue Gray was asked to lead an inquiry.
She had been due to produce her full report into the parties last month, but had to delay publication when the police announced their own investigation.
Instead Gray released her initial findings in which she criticised "failures of leadership and judgement" in government.
The police have been looking into 12 of the 16 events listed in her report. Johnson is known to have attended at least three of the gatherings:
- 20 May 2020 in the Downing Street garden
- 19 June 2020 in the Cabinet Room for the prime minister's birthday
- 13 November 2020 on the departure of a special adviser
Photo file Caption: United Kingdom PM Boris Johnson