A FORGED letter allowed demonstrators to storm the Commons chamber and overshadow a vote that brought fox hunting to the brink of an outright ban, MPs were told last night.

The five pro-hunt protestors, who threatened ministers at the Dispatch Box in an unprecedented security breach, were led to the entrance of the chamber by a Commons passholder.

But an investigation has not yet revealed who was responsible for helping the protestors, Speaker Michael Martin told the Commons in an emergency statement.

Last night, an investigation was still ongoing into the lapse, amid claims that no members of the public had managed to invade the chamber for 350 years - since the time of King Charles 1.

One of the protestors was named as Otis Ferry, the 21-year-old son of Bryan Ferry - who was born in Washington, Wearside - lead singer of Roxy Music.

And last night it was revealed that Otis Ferry had contacted a BBC reporter before the protest to say they had staged a dry run on Tuesday.

He told the reporter of the plan to storm the Commons, but the information was not passed on.

Last Saturday, Mr Ferry - who spent four seasons as a kennelman and assistant whipper-in with the Middleton hunt in Birdsall, North Yorkshire - joined a protest outside Tony Blair's constituency home in Trimdon, County Durham.

There were violent clashes yesterday outside Parliament where an estimated 10,000 pro-hunters gathered, waving banners demanding "No Ban".

Smoke bombs were thrown at the police, who responded by striking demonstrators with batons. Nineteen people were believed to have been injured, including two police officers.

The scenes in the chamber - which forced the sitting to be abandoned for 25 minutes - distracted attention from MPs voting, by a majority of 190, to outlaw fox hunting and hare coursing.

Later, they voted to delay the introduction of the hunting ban from three months to the end of July 2006 - past the last possible date of the next General Election.

The Bill now goes to the Lords, which is expected to continue to oppose the ban. The Government will then use the Parliament Act to force the measure through.

Last night, there were reports that the invading protestors had got past security by wearing builders' overalls, later found in a committee room.

Once inside the chamber, wearing T-shirts portraying Tony Blair with horns, they screamed abuse.

They were quickly wrestled to the floor by attendants and bundled out of the chamber.

One Labour MP said he would be "very, very surprised if this wasn't an inside job" - suggesting a researcher for a pro-hunting MP might have helped them gain access.

It was the third major security breach at Parliament in six months, after two men scaled Big Ben in a protest to mark the Iraq war in March and flour bombs were thrown into the chamber in May.

And it came only 48 hours after a Fathers 4 Justice protestor, dressed as Batman, scaled the walls of Buckingham Palace.

Describing the latest security lapse as "deadly serious", Peter Hain, the Leader of the House, revealed that armed police were immediately stationed outside the chamber.

Alan Michael, the Rural Affairs Minister, called on the Countryside Alliance to "lower the temperature".

John Greenway, Tory MP for Ryedale, North Yorkshire, warned that the Government would reap a whirlwind at the next election.

"Millions of people know that, if this ban goes through, then shooting and angling will be next," he said.