A protester was in police custody on Monday after he camped out all night on the roof of Labour Party Deputy Leader Harriet Harman's south London home, forcing her to move out.

The 49-year-old from the Fathers 4 Justice protest group scaled the building at the weekend to demand divorced fathers be given better access to their children.

The man, who has not been named by police, joined another protester who was still on the roof early on Monday.

"A 49-year-old man who came down from the roof is in custody," a Scotland Yard spokeswoman said.

"A second man remains on the roof."

The protest was the latest in a line of high profile stunts by the group, which has included pelting then Prime Minister Tony Blair with condoms full of purple flour in the House of Commons debating chamber in 2006.

On Sunday, police surrounded Harman's house in Herne Hill and waited for the two costumed men, who said they had enough food for a week, to come down.

Harman told reporters as she moved out: "I don't think it is fair to the police resources to be tied up outside my house because of this demonstration when they could be doing other important policing work."

"I also think it is unfair on the neighbours, so we are moving out," she said, adding that although the protesters said they wanted to meet her they had made no attempt to do so.

The two protesters, clad as comic superheroes, had hung a banner down the side of the house reading "A father is for life, not just conception."

Fathers 4 Justice founder Matt O'Connor, who was not in the rooftop protest, told Reuters the pair had simply walked into Harman's garden while she was at home and used a ladder to climb onto the roof.