The crowd were seen chanting “this is a work event” and “my name is Boris”, the former in reference to the prime minister's excuse for having attended an earlier party on 20 May 2020.
Footage shows the imitators of Mr Johnson holding several different types of alcohol with some of them wearing union jacks around their shoulders.
Police said officers moved along a group of around 50 people outside Downing Street at around 1pm on Friday, adding that no arrests were made.
An inquiry is looking into allegations of several parties held in Westminster during periods of strict Covid restrictions, including the 20 May event which the prime minster has apologised for attending.
Pressure has been building on the prime minister as public opinion has soured since allegations of potential lockdown rule breaking emerged towards the end of last year.
He has faced several calls to resign from members of his own party.
His apology for attending what he said he thought was “a work event” has been widley mocked and has spawned dozens of internet memes.
Labour leader Sir Keir Starmer said the prime minister’s excuse was “so ridiculous that it’s actually offensive to the British public”.
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