The MP Eric Joyce has been arrested after police were called to a fight in a bar at the House of Commons.
The independent Member of Parliament for Falkirk was held after the incident at the Sports and Social Club bar.
A Metropolitan Police spokesman said: "Police were called shortly before 10.30pm this evening to reports of a disturbance at a bar within the House of Commons.
"Officers attended and a man aged in his 50s was arrested in connection with this incident. He remains in custody and inquiries continue."
Joyce resigned from the Labour Party after headbutting Tory rivals Stuart Andrew and Ben Maney in a different Commons bar last February.
On that occasion the 52-year-old also punched Tory councillor Luke Mackenzie and Labour whip Phillip Wilson and insulted police officers.
After leaving Mr Andrew with a bloodied nose, Joyce told police: "He deserved it."
Joyce, who accepted he was "hammered" on red wine during the brawl, launched into a frenzied attack after shouting that the Strangers' Bar "was full of ******* Tories".
The former soldier walked away from Westminster Magistrates Court with a fine and pub banning order after admitting four counts of common assault.
He was fined £3,000 and ordered to pay £1,400 to victims after he entered early guilty pleas.
Joyce was also given a 12-month community order - banning him from entering pubs and licensed premises for three months - and imposed with a curfew order from Friday to Sunday.
After the hearing, Joyce admitted he was lucky not to be jailed and said he was "deeply apologetic".