A Fathers 4 Justice protester dressed as Santa who chained himself to a lamp above the gates to Buckingham Palace has been arrested by police.
The stunt was part of a 'Christmas campaign' by Fathers 4 Justice
The activist, named by the group as Dave Pyke, 49, was chained to the lamp for almost two hours before police brought him down.
The standard is flying at the palace, indicating the Queen is at home.
A protester from the same group climbed onto the Palace balcony in September. Mr Pyke was also involved then.
Fathers 4 Justice is engaged in a long-running campaign of stunts in an effort to get reform of the laws governing divorced fathers' access to their children.
Bystanders gathered at the Queen Victoria Memorial to watch Tuesday's incident, as 20 police maintained a cordon.
Shortly after 1600 GMT two officers were raised on a cherry picker to bring Mr Pyke down.
Mr Pyke, from Cheltenham, Gloucestershire, waved and smiled at supporters and spectators as he was strapped into a safety harness for his descent.
A Metropolitan Police spokesman said Mr Pyke was arrested after he was cut free of his chains and is being held by police in central London.
"He has been arrested on suspicion of causing criminal damage and also causing a public nuisance," the spokesman said.
A Fathers 4 Justice spokesman said Mr Pyke had started to climb the gates at 1415 GMT. He climbed about 20ft up a pillar.
The group said Mr Pyke had been one of its members for 12 months and was its Gloucestershire co-ordinator.
It said he was protesting about not being able to see his children.
The stunt marks the beginning of its campaign called Put the Fathers Back into Christmas, said group spokesman Matt O'Connor.
Activist Dave Pyke also tried to get onto the Palace in September
He said Mr Pyke was dressed as Santa Claus to show the protest was in "good humour".
Another campaigner, Jason Hatch, said the original plan had been for Mr Pyke to climb on to the Queen's carriage as she returned to the palace after delivering her speech to Parliament, but that had been ruled out as "inappropriate".
A Palace spokesman said: "Christmas appears to have come early."
Mr O'Connor said Mr Pyke had been angered by a BBC Real Story programme last night, which discussed Fathers 4 Justice and suggested violent fathers were being allowed access to their children because of the campaign.
In September's incident, Mr Pyke, dressed as Batman's sidekick Robin, attempted to get onto the palace balcony using a ladder.
He was ordered down by armed police who are believed to have threatened to shoot him. But Mr Hatch, who was dressed as Batman, managed to climb on to the balcony.
Electric fencing has been installed since that protest which prevented Mr Pyke from climbing on to the balcony on Tuesday.