By Ian Dunt Follow @IanDunt
Labour MP Eric Joyce has been suspended from the party following reports of an altercation in a Commons bar last night.
Police were called to the scene after reports of a fight in the Strangers Bar, which is reserved for MPs and their guests.
"We were called at approximately 10:50 GMT last night to reports of a disturbance at a bar within the House of Commons," a Scotland Yard spokesman said.
"A man aged in his 50s was arrested by officers on suspicion of assault. He remains in custody in a central London police station. Inquiries are continuing."
Tory MP Stuart Andrew has reportedly alleged he was headbutted and punched by the Labour MP for Falkirk.
Ed Miliband reportedly took the decision to suspend the MP himself and is recieving reports on the altercation, which may have involved several MPs.
A Labour party spokesman said: "This is an extremely serious incident. We have suspended Eric Joyce pending the results of the police investigation."
Mr Joyce served in the Army Education Corps before entering politics. He was parliamentary private secretary to defence secretary Bob Ainsworth until 2009, when he quit over concerns around the Afghan war.
He also resigned as Northern Ireland minister after pleading guilty to failing to provide a breath test a year later.
The event follows a 2010 fight in the Sports and Social Club, also in parliament, in which Labour MP Paul Farrelly was said to have wrestled a man to the floor during a karaoke evening.