Three men have been arrested after costumed Fathers 4 Justice protesters scaled a Foreign Office balcony overlooking Downing Street.
The protest by Fathers 4 Justice follows a series of similar stunts
The Robin, Batman and Captain America protesters timed the stunt to coincide with Labour's announcement on "family-friendly" working on Monday.
They unfurled a banner saying: "Don't let Labour stop you being a Superdad."
The trio spent Monday afternoon and evening perched 50ft above the junction of Downing Street and Whitehall.
Just before 2200 GMT, one of the protesters climbed into the Foreign Office, where police were waiting.
The two others followed later, Scotland Yard said.
A police spokeswoman said there had been "no breach of security", and the men could not have accessed the Foreign and Commonwealth Office or any of the buildings within Downing Street.
The campaign group has already breached security at Buckingham Palace and the House of Commons in its campaign for fathers to have better access rights to their children.
The London co-ordinator for Fathers 4 Justice, Richard Castle, said the three men were "hardened protesters" who had planned to stay up on the balcony as long as possible, having got onto the building via a ladder mounted on a flatbed truck.
He added that the person dressed as Batman was Jason Hatch, who was behind the Buckingham Palace protest.
And he pledged the campaign group would undertake a series of stunts in the run up to the general election, predicted to be held on 5 May.
"What we are trying to highlight is that rather than helping families and children, the government is failing families," Mr Castle said.
The protesters were on a ledge 50ft above Downing Street
"They are producing a generation of McDads - fathers who only ever see their children in McDonalds once every few weeks."
Women's Minister Patricia Hewitt said the government would not give in to the group's key demand for a 50/50 share of access between mother and father.
"Children are not property to be divided 50-50 like the goods divided between a couple on divorce," she said.
"What we have recently put forward are proposals that will give children much more time with both their parents - the non-resident parent as well as the resident parent."
Fathers 4 Justice founder Matt O'Connor identified the protester dressed as Robin as Andy James though he added he did not the know the identity of the Captain America demonstrator.
Mr O'Connor added that he was surprised at the ease by which they managed to clamber onto the building.
"It was a breeze," he said.