The parties in Downing Street, which have caused outrage and sparked calls for Boris Johnson to resign, are already being investigated by a senior civil servant.
Police say they will now investigate whether lockdown parties at the heart of the UK government broke COVID-19 rules.
It was confirmed by Cressida Dick, commissioner of the Metropolitan Police, on Tuesday morning.
The parties, which have rocked Prime Minister Boris Johnson's Conservative government and sparked calls for him to resign, are already being investigated by senior civil servant Sue Gray who is expected to release a report at the end of the month.
"I can confirm that the Met is now investigating a number of events that took place at Downing Street and Whitehall in the last two years in relation to potential breaches of COVID-19 regulations," she told the London Assembly's police and crime committee.
The investigation does not mean that "fixed penalty notices" will be issued in every instance and to every person involved. She said the force had tried to take a "proportionate approach" to the allegations.
The decision to investigate came after the Cabinet Office provided outline findings from its inquiry to police.
The Metropolitan Police wrote "to the Cabinet Office this morning with a formal request for it to refer all relevant information gathered from its inquiry in relation to events on the dates in question to support the police investigations," police said in a statement.
A number of revelations have emerged in the press detailing gatherings held among Johnson's staff that appear to have breached lockdown restrictions when they were held.
In the most recent allegation, it emerged that a birthday party was held for Johnson inside Downing Street during the first COVID-19 lockdown. At the time, restrictions allowed for gatherings of only up to six people and indoor gatherings were banned.
The prime minister had apologised on 12 January over the alleged gatherings but continued to defend his actions, stating that he believed a "bring your own booze" garden party on 20 May was a work event.
Days later, Johnson said nobody told him that the 20 May gathering was against COVID-19 rules.
The parties have prompted opposition lawmakers to call for Johnson to resign, with some calling the prime minister's defence "ludicrous."
"First he claimed there were no parties, then he wasn’t present, then he admitted he was at them but he didn't know it was a party and then Mr Speaker, the latest sorry excuse is really the most pathetic of them all. Nobody told me. Nobody told me. Nobody told the prime minister he was breaking his own rules. Absolutely pathetic," said Ian Blackford, the leader of the Scottish National Party, in Westminster last week.
There are now some members of Johnson's own party calling for him to step down, with a Conservative MP defecting to the opposition Labour party ahead of PMQs last Wednesday.
Another Conservative MP, David Davis, said he expected leaders "to shoulder the responsibility for the actions they take" but that Johnson had done the opposite of that.
Reminding the prime minister of a quotation from an MP to Neville Chamberlain, Davis said: "You’ve sat there too long for all the good you’ve done, in the name of God, go."