Labour MP Clive Lewis has apologised after the emergence of video footage that shows him at a Momentum event, saying: “Get on your knees b****”.

The video shows the MP for Norwich South on stage during the closing hours of the World Transformed festival in Brighton, an event held alongside the Labour Party conference last month.

The crowd responds noisily to Mr Lewis’s comment – which was directed at a man and apparently intended as a joke – with one person present heard saying: “This is meant to be a safe space, thank you.”

Mr Lewis made the comments to Sam Swann, a 28-year-old actor, who was kneeling down on stage to take the score during a game show segment at the event.

Mr Swann told The Independent: “He says to me ‘on your knees b****’ and it is clearly jovial.

“The whole event was so brilliant for seeing MPs letting their hair down and f******* around with people who support them. I think Clive Lewis is an absolute legend.”

But posting a link to the video, which surfaced on Guido Fawkes, an online political blog, the Conservative MP Mims Davies said it was “astounding, inappropriate language” from Mr Lewis. “I think Jess Phillips needs to get you on an urgent training course,” she added. “This must stop.”

Moments later, Ms Phillips, the Labour MP for Birmingham Yardley, posted on Twitter: “Just seen the Clive Lewis video. Obviously I’m appalled, just listened to seven teenage girls speak up about gender inequality. Perhaps I’ll bring them to work on Monday.”

Her comments were echoed by the senior Labour MP Yvette Cooper, who chairs Parliament’s Home Affairs Select Committee. “No excuse for saying this, whatever context,” she said.

The party’s former deputy leader Harriet Harman added: “Inexplicable. Inexcusable. Dismayed.”

Shortly after the footage emerged, Mr Lewis said on Twitter: “I apologise unreservedly for the language I used at an event in Brighton last month. It was offensive and unacceptable.”