The former treasury minister, 54, was left covered in blood after the attack at the session in Newham, east London, on Friday afternoon.

He is recovering in hospital where his injuries are not said to be life-threatening.

A 21-year-old woman was arrested at the scene and is being questioned at a nearby police station. Scotland Yard said a knife had been recovered.

It is understood one of the MP's assistants, Andrew Bazeley, disarmed the attacker before a security guard restrained her.

A witness at the surgery in Beckton Globe library said she saw Mr Timms being carried into a room wearing a bloodstained shirt.

Speaking outside the library, the girl, who did not wish to be named, said: "I saw an Asian woman and a security guard was holding her.

"I saw everyone screaming and there was a woman with a buggy who was really crying."There was a bit of blood on the floor. It was quite dramatic. I saw him being dragged into another room. There was blood on his shirt."

Mayor of Newham Sir Robin Wales added: "My understanding is there was an appointment made for the woman. At the beginning of the interview she stabbed him. The security guard came in and disarmed her and held her until the police arrived."

Mr Timms, who has been MP for the East Ham constituency - and previously for Newham North East - since 1994, was taken by ambulance to the Royal London Hospital where he was due to undergo exploratory surgery.