Protesters stormed the Oxford Union last night, delaying the start of controversial free speech debate.

About 1,000 people turned up to protest against the appearance of BNP leader Nick Griffin and historian David Irving.

The pressure-cooker atmosphere eventually boiled over minutes before the forum was due to start in the debating chamber.

Security was stretched as dozens of protesters managed to clambered over the railings of the Union building in St Michael's Street.

Other protesters surged through the Union's main gate and stormed into the debating chamber, where they staged a sit-in.

Abu Ali Mustapha, 21, from Manchester, said: "There was a mass demonstration and hundreds scaled the gates and pushed through the door. I feel our demonstration was victorious."

The Union had drafted in extra security for the event, with every single visitor asked to produce identification, which was then scanned.

The entrance to the building was closed ahead of schedule because of security fears and Union members attempted to barricade the doors to prevent the crowd from breaking into the chamber.

At least 40 people were involved in a 10-minute scrum at the main doors of the building. No-one was thought to have been injured.

Katie Smart, 20, an Oxford Union member who was waiting for the debate to start, said: "It was terrifying."

Outside the venue, around 20 members of Antifa - an anti-fascist group - pounded along Cornmarket Street to join the crowd. One member, who was dressed in black, with his face covered, said: "We have come to confront the BNP."

Protesters bellowed anti-fascist slogans, while one sat down and played a piano in the corner of the room. The sit-in lasted 15 minutes.

Mr Griffin, who was supplied with water and chocolate in the Morris Room during the scuffle, said: "They are just showing themselves up for what they really are.

"This should serve as a wake-up call to people about just how unpleasant the far left is."

The event eventually got under way, with Mr Griffin debating with students in the Macmillan Room and Mr Irving in the main chamber.

Mr Griffin was given a round of applause by 100 people following his eight-minute speech.

He told the Oxford Mail: "That is a mob outside that would kill perfectly happily. There's only 1,000 of them. It's a hideous mentality."

Oxford Union president Luke Tryl said: "It has been very stressful. There were people chanting 'Kill Tryl'. I felt awful. It appalls me that they were willing to push and kick their way in through the door to stop these people speaking."

Martin McCluskey, president of the Oxford University Student Union, said it was "disgraceful" that Mr Griffin and Mr Irving had been given the same platform as past speakers at the Union, such as Mother Theresa and the Dalai Lama.

By Oxford West and Abingdon Liberal Democrat Liberal Democrat MP Dr Evan Harris said stopping the pair speaking would have risked turning "bigots into martyrs".