Eric Joyce, Labour MP, has been arrested after headbutting a Tory MP and attacking several other Conservatives in the Strangers Bar in the Commons.
The Tory victim is said to be Stuart Andrew, MP for Pudsey, along with two other Conservative MPs and one Labour MP.
The attack came at the end of a long day of fiery debate in the Commons regarding the controversial Health Bill.
PoliticsHome website quotes sources as saying Joyce had complained that the bar was "full of Tories".
A Scotland Yard spokesperson confirmed:
While the bar is always full of MPs on days that the Commons sit, last night other guests included the Speaker of the House of Commons in Canada, Andrew Scheer.
Mr Joyce, the MP for Falkirk, has been the subject of controversy before, resigning as shadow minister for Northern Ireland after failing to provide a breath test in 2010.
He was suspended from the Labour Party until the completion of a police investigation into the alleged assault.