The leader of the Commons has demanded a report into how two Greenpeace activists managed to climb Big Ben during Saturday's anti-war protests.

The Greenpeace campaigners - brothers Harry and Simon Westaway from East Sussex - staged a six-hour protest after clearing a wall and security fence to reach the famous tower.

Both described their feat as "easy".

They were arrested on suspicion of causing criminal damage, but have been bailed to return to a London police station in April.

Speaking on Sunday, Peter Hain said he was "very disturbed" that the brothers were able to reach Big Ben so easily.

"It is a huge embarrassment, both to the House authorities and the policing arrangements," he said.

"Twenty or 30 years ago an audacious protest like that by Greenpeace would have been seen for exactly that. But what if these had been suicide bombers?"

"I am very disturbed about it and I want an urgent report as leader of the Commons about how it happened," he added.

"Indeed only last week we had a detailed planning meeting to have a proper security review, to make sure that we are absolutely certain that the House can be properly protected."

Conservative defence spokesman Keith Simpson described the incident as a "wake up call" for security arrangements and a "dangerous embarrassment" both for the Palace of Westminster and the Metropolitan Police.

Liberal Democrat home affairs spokesman Mark Oaten said it raised "obvious questions for security".

However, while Metropolitan Police commander Brian Paddick has ordered an "automatic review" of security arrangements, he insisted there was no danger of the brothers entering the building.

"Yes, they could have left something there and run away but at the end of the day they could not have caused any breach of security in terms of threat to life, in terms of blowing up anything of importance just inside the perimeter fence."

Alarms were triggered as they should be when the men climbed the fence, he added.