The brothers' stunt has prompted calls for improved security

Harry Westaway, 28, and his brother Simon, 23, both from Lewes in East Sussex, had been arrested on suspicion of causing criminal damage.

The Greenpeace activists spent seven hours on the London landmark on Saturday and said breaching Parliamentary security had been "easy."

Their actions have prompted a series of calls for security improvements.

The brothers cleared a wall and security fence before beginning their climb up the 315-ft tower wearing protective helmets and harnesses at about 0615 GMT.

It is a huge embarrassment, both to the House authorities and the policing arrangements Peter Hain, Leader of the House of Commons UK 'not ready for terror attack'

They stayed on a ledge below the clock face for several hours before coming down just before 1300 GMT when winds become too strong.

They were arrested when they ended their protest, but were released on bail later and must return to a police station in central London next month.

The incident has started a wide range of calls for improved security or an inquiry into how the brothers were able to carry out the stunt.

Metropolitan Police Commander Brian Paddick announced their would be an "automatic" review of security.

The brothers scaled a wall and fence before climbing the tower

Glen Smythe, chairman of the Metropolitan Police Federation said Greenpeace should be condemned for the "extremely foolish" act.

And speaking on BBC1's Breakfast With Frost programme, Leader of the House of Commons Peter Hain demanded an urgent report into the incident.

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

"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?

"So I am very disturbed about it and I want an urgent report as Leader of the Commons about how it happened."