Shamed Falkirk MP Eric Joyce is being held by police following another late-night brawl at a bar in the House of Commons.

The independent MP, who quit Labour after being fined last year for assaulting Tories at another parliamentary bar, was arrested after the incident at the Sports and Social Club bar.

Joyce is due to stand down at the general election in 2015, but last night's events will increase the pressure on him - and parliament - to leave before then, causing a by-election which would be fiercely contested by Labour and the SNP.

Asked whether the Prime Minister felt Mr Joyce could continue as an MP, David Cameron's official spokesman told a regular Westminster media briefing: "That is a matter for Mr Joyce."

A Metropolitan Police spokesman said last night: "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 while inquiries continue, the Met said today.

Tony Grew, from the PoliticsHome website, witnessed the altercation, which he said happened during a karaoke night in the bar, which was packed with about 150 people.

He said Joyce entered the room "obviously agitated" and pushed his way forward to the bar.

When he followed him out of the bar he saw Joyce on the ground "wrestling with two police officers".

"He appeared to have one of the officers in an armlock, he put his arm around the officer's neck, and the other police officer was on top of him," Mr Grew.

"There were around at least 40 or 50 parliamentary staff, shocked, watching this melee as it occurred. Bar staff were trying to push people back, telling them to stand back and let the police do their work."

Mr Grew added: "I can vividly remember a policeman's hat rolling on the ground towards me as I was watching this scene unfold."

He said that after Joyce was handcuffed he saw him "on a bench, being held down by three or four police officers - he was still struggling."

Mr Grew suggested the altercation could have occurred because Joyce became upset that he was not allowed to take a glass outside into the smoking area.

One MP expressed concern for Joyce's welfare. Tory Penny Mordaunt wrote on Twitter: "MPs done great stuff for mental health but must ensure that colleagues who need help get it, esp if they are now sans party."

Joyce resigned from the Labour Party after headbutting Tory rivals Stuart Andrew and Ben Maney in a previous incident in a Commons bar last February.

The 52-year-old also punched Tory councillor Luke Mackenzie and Labour whip Phillip Wilson while going berserk and calling officers "c****".

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 f****** 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 to avoid jail and said he was "deeply apologetic".