A member of House of Commons staff was arrested after a fight outside one of Parliament’s busiest bars.
The Sports and Social Club has been closed and a 57-year-old man arrested on suspicion of GBH and affray.
Police later released the man, who remains under investigation.
A 64-year-old man, also a Commons employee, is reported to have been taken to hospital in an ambulance following the incident.
He needed treatment for non-life threatening injuries.
Scotland Yard said police were still investigating what happened but no-one else was thought to have been involved.
A House of Lords spokesperson said the Sports and Social Club bar would stay closed until the investigation was complete.
The venue, which is a popular haunt for MPs and their staff, is a large traditional pub in the bowels of the Parliamentary estate.
It was recently taken back under the direct control of the House of Lords authorities from an outside contractor and its future was already thought to be in doubt.
Man arrested after fight outside Parliamentary bar}