A Channel 4 presenter was caught on camera calling a government minister a "c***" outside 10 Downing Street.
Krishnan Guru-Murthy could be heard making the slur to Tory Steve Baker before laughing in a clip that has been widely shared on social media tonight.
Minister for Northern Ireland Mr Baker has since called for the veteran broadcaster to be sacked if it's proved he's "in breach of his code of conduct".
The presenter then apologised after what he described as a "robust" exchange.
In a 20-second snippet from the stream, the camera is pointing at a police officer standing guard outside the Prime Minister's home after Suella Braverman resigned as Home Secretary.
It's not clear if Mr Guru-Murthy realizes he's still miked up as he says off-camera: "Thanks a lot, Steve."
Mr Baker's response can't be heard before the presenter continues: "It wasn't a stupid question, Steve, you know it. I'm very happy to go up against you on [PM Liz] Truss any day."
He then laughs before saying: "What a c***".
Mr Baker has since told Times Radio it’s "most unfortunate" Mr Guru-Murthy swore on tape, adding: "If it’s in breach of his code of conduct I hope they sack him."
Mr Guru-Murthy then tweeted: "After a robust interview with Steve Baker MP I used a very offensive word in an unguarded moment off air.
"While it was not broadcast that word in any context is beneath the standards I set myself and I apologise unreservedly.
"I have reached out to Steve Baker to say sorry."
Braverman dramatically stepped down from her Cabinet position after admitting to sending an official document from her personal email.
In another blow to Ms Truss's embattled government, the ex-Cabinet minister said in a letter "it is right for me to go" and accepted responsibility for "a mistake".
It is understood the Cabinet Secretary Simon Case found two breaches of the ministerial code, including using a personal email and sending sensitive information to someone outside government.
Ms Braverman also took a departing shot at the Prime Minister and revealed she had "concerns about the direction of this government" after days of extraordinary turmoil.
Ms Braverman said: "Not only have we broken key pledges that were promised to our voters, but I have had serious concerns about this Government's commitment to honouring manifesto commitments"
The former Cabinet minister added: "Pretending we haven't made mistakes, carrying on as if everyone can't see we have made them and hoping that things will magically come right is not serious politics.
In a short response to Ms Braverman, the Prime Minister praised her work at the Home Office, but said: "I accept your resignation and respect the decision you have made.
"It is important that the Ministerial Code is upheld, and the Cabinet confidentiality is respected".
Around an hour after her resignation, No10 also announced Ms Braverman had been replaced by the ex-transport secretary Grant Shapps - an ally of Rishi Sunak.
The extraordinary development means Ms Truss has lost both her Chancellor Kwasi Kwarteng and her Home Secretary in the first 50 days of her administration.
It came after the Prime Minister also cancelled a planned visit to Hertfordshire, with No10 failing to give a specific explanation beyond "government business".
The Mirror has approached Channel 4 for comment.
