A Labour shadow minister is facing an internal party investigation after it was alleged that he swore at a colleague.
Shadow minister Clive Lewis was reported to the party's chief whip by fellow Labour MP John Woodcock after the pair got into an altercation in a corridor on Tuesday night.
BuzzFeed News understands Lewis is set to speak to the whip about the argument on Wednesday.
Woodcock, who plans to vote in favour of airstrikes on ISIS targets in Syria, was unimpressed by comments Lewis had made to the BBC and challenged him in Portcullis House, where MPs have their offices.
Referring to MPs who planned to back the government's motion, Lewis had told the BBC: "On their heads be it."
Several Labour MPs in favour of the government's motion have faced online abuse and threats of deselection, and a number of comments by Jeremy Corbyn and his allies have been interpreted as encouraging this behaviour.
A source told BuzzFeed News that during their discussion, Lewis started shouting at Woodcock. "You want to start this, we'll finish it, so fuck you," Lewis said.
Writing on Twitter, Woodcock said he was "not going to be intimidated".
In a statement, Lewis told BuzzFeed News that he regretted swearing at Woodcock and would be happy to apologise.
He said: "On leaving a colleague’s office in Portcullis House I encountered John who approached me and began to harangue me about comments I had made the previous day.
"I explained to him that some of my comments had been reported out of context. Unsatisfied with my response, he continued with the confrontation, so shortly afterwards, I walked away feeling this to be a futile exchange.
"As I left I did indeed swear at him which in hindsight I regret. I’m more than happy to apologise to John, I’d like to think he’d be able to do the same back."
A Labour spokesperson said: “We cannot comment on individual complaints, but all Labour members and representatives are expected to uphold the highest standard of conduct at all times.”