Britain's opposition Labour party suspended a lawmaker on Thursday after he was arrested following a late-night brawl in the House of Commons, which reportedly involved a rival Conservative MP.

"This is an extremely serious incident. We have suspended Eric Joyce pending the results of the police investigation," a Labour party spokesman said.

Police confirmed that they had arrested a man in his 50s following a disturbance at a bar in the House of Commons.

Media reports said Stuart Andrew, a lawmaker from Prime Minister David Cameron's ruling Conservative party, claimed to have been headbutted in the incident, although neither his office nor Joyce's would comment.

A police spokesman said: "We were called at approximately 10:50 pm last night to reports of a disturbance at a bar within the House of Commons.

"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."

Joyce, 51, has been the member of parliament for Falkirk in Scotland since 2000, and before that he served in the army.

In the Commons chamber on Thursday, Speaker John Bercow said: "Members will be aware of reports of a serious incident in the House last night.

"I have been informed by the serjeant at arms that the honourable member for Falkirk has been detained in police custody.

"The matter is being investigated. I take this matter very seriously, as do the House authorities. I would ask that no further reference should be made to these reports in the Chamber today."