A Fathers 4 Justice campaigner dressed as Batman has been removed after staging a five-hour protest on a ledge by the Buckingham Palace balcony.
The intruder spent about five hours on the ledge
Jason Hatch, 33, entered the grounds and scaled a wall at 1420 BST.
Police moved Mr Hatch onto a "cherry-picker" crane beneath the ledge at 1915 BST after hours of negotiation.
In a statement to the House of Commons, the Home Secretary said the police had "acted correctly" but the need for more security was under urgent review.
David Blunkett said: "The speed with which the intruders were able to scale the wall is of concern."
HOW INTRUDER REACHED ROYAL BALCONY
1 Protesters create a diversion at the front gates of the palace.
2 "Batman" and "Robin" climb over low fence at side of palace grounds while security staff are distracted.
3 "Batman" climbs up a ladder on to the roof of an adjoining building. "Robin" comes down after police threaten to shoot him.
4 "Batman" shuffles from roof along ledge to the edge of the royal balcony, where he stages his high-profile protest.
He added the protesters had done their "very reasonable" cause a disservice by acting in a "foolish and silly" way.
Shadow home secretary David Davis responded with heavy criticism of the Home Office, describing repeated breaches of royal security as "scandalous incompetence".
Liberal Democrat chairman Mark Oaten said the situation was "at best highly embarrassing and at worst could have had terrible consequences".
Met chief Sir John Stevens said police would have shot the protester if he had been judged a terror risk.
He has also described the security breach at the Palace as "unacceptable".
Mr Hatch, from Cheltenham, Gloucestershire, is understood to have scaled a wall of the palace at one side - where it met the security fence - using a ladder, while others caused a distraction at the main gate.
He then unfurled a banner which read "Super dads of fathers 4 justice".
Cheers of encouragement
After being brought back to the ground on the crane, Mr Hatch was put into a police van and taken away from the Palace, to cheers of encouragement from a small crowd of supporters.
The latest broaching of palace security follows other incidents, including one in which a reporter got a job as a royal servant. In addition, Prince William's 21st birthday party at Windsor Castle was gatecrashed.
Mr Hatch was accompanied in his scaling of the walls by at least one other activist.
Dave Pyke, 48, who was dressed as Batman's sidekick Robin, is understood to have stopped climbing the ladder onto the roof, after being threatened by armed police.
He was later arrested as he gave an interview to Sky News.
Before his arrest, he told BBC News Online: "We are totally untrained, just ordinary guys and if we can get in there, anybody can get in there."
Mr Pyke added: "I thought I would be pounced on by the police. I went over to the park and put on
a coat and cap and came back."
Fathers 4 Justice was set up by fathers who have either no access, or very limited access, to their children and feel they have been treated unfairly by courts.
Monday's Buckingham Palace stunt is the latest in a high-profile series by the group's costumed campaigners who have protested on the London Eye and the Church of England General Synod in York. Mr Hatch was understood to have taken part in the York protest.
It is thought he has two children, aged four and five, who he has not seen for several years.
Fathers 4 Justice spokesman Matt O'Connor said the incident was to highlight Monday's court appearance of a campaigner accused of staging a flour-throwing protest in the House of Commons.
The Queen was not at the palace as she is at Balmoral in Scotland, a palace spokeswoman said.
Sir John Stevens explained police had made a split-second judgement that Mr Hatch was not a security risk because of the way he was behaving and the clothes he was wearing - and for this reason they did not open fire.
Large numbers of police were around the palace while the incident continued, with a helicopter hovering overhead.
About two dozen supporters mingled with the media scrum during the afternoon, cheering and blowing klaxons to waving from Mr Hatch.
Bemused tourists also looked on as negotiators tried to get the activist down.