Resurfaced video footage from 1992 shows then-reporter Boris Johnson swearing at a lighting operator while he tries to work.
It comes as Mr Johnson – now prime minister of the UK – told schoolchildren on Tuesday that journalists spend their time “attacking” and “abusing” people.
The 14-second clip was shot in a Denmark press room at the height of the Maastricht Treaty referendum, and shared by BBC News producer Bruno Boelpaep on Twitter.
“Nice bit of archive from the #BBC Brussels tape library found by cameraman Phil Goodwin,” Mr Boelpaep said when he shared it last year.
Reporters from newspapers all around the world can be seen typing away in the video, with a busy 27-year-old Mr Johnson – then Brussels correspondent at The Daily Telegraph – very much the focus of the camera’s shot.
It is only when a lighting operator, who cannot be seen, shines a bright white light on the room that the future Conservative Party leader loses his temper and begins flailing his arms in the air, before saying: “Oh, p*** off!”
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The light quickly turns off and Mr Johnson resumes his writing.
In a visit to a southeast London school earlier, almost 29 years after the footage was filmed, the PM suggested to pupils it was the “guilt” of being a journalist that led him to swap the profession for politics.
“I was a journalist for a long time,” he said during a discussion at Sedgehill Academy in Lewisham.
“But when you’re a journalist, it’s a great, great job, it’s a great profession, but the trouble is that you sometimes find yourself always abusing people or attacking people.
“Not that you want to abuse them or attack them, but being critical when maybe you feel sometimes a bit guilty about that because you haven’t put yourself in the place of the person you're criticising.
“So, I thought I'd give it (politics) a go.”
"Piss off!" not happy about the cameraman's light in the press room, @BorisJohnson then 27 & @Telegraph EU correspondent,covering the referendum on Maastricht Treaty in Denmark,1992🇪🇺
Nice bit of archive from the #BBC Brussels tape library found by cameraman Phil Goodwin 🎥 pic.twitter.com/xAW03XqKZG
— Bruno Boelpaep (@BrunoBoelpaep) March 5, 2020
He added that he was in his mid-30s before he went into politics and his “strong” advice would be that anyone considering a political career do something else first.
Mr Johnson’s press secretary, herself a former journalist, Allegra Stratton later denied the PM’s remarks were an indirect comment on recent press reports about the position his fiancée, Carrie Symonds, holds in the government.
“That is the prime minister talking about the fact that for all of you as journalists, your job is to constantly challenge and that’s something that makes all of us in government better,” she told a Westminster media briefing.
“The role of journalism is to constantly be asking the details and the finer points, as you have done on the roadmap.”
Mr Johnson held numerous posts as a journalist, including as a columnist for The Telegraph and editor of The Spectator magazine between 1999 and 2005.
He faced major backlash in 2018 for one of his columns in which he likened women who wear face coverings, such as burkas, to “letterboxes”.
The PM was also criticised on a separate occasion for calling black people “piccaninnies” and writing they had “watermelon smiles”.
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