A fathers' rights activist who spent nearly eight hours on a roof at Buckingham Palace said taking a bullet "would have been worth the risk".
Martin Matthews, 48, and Bobby Smith, 33, managed to breach security by using a ladder to scale the roof of the Queen's Gallery at around 3.15pm.
The pair were able to climb on top of the public art gallery despite a number of police officers nearby, Mr Matthews said.
Speaking from the roof, he told the Press Association: "We parked a road away and came with a long ladder and walked past a number of armed policemen. They presumed we were workmen".
Mr Matthews said he was aware of the risks he was taking in light of heightened security concerns following the Paris terror attacks.
"Obviously there were a few concerns. People are going to be nervous at the moment," he said.
"But even if I had taken a bullet, it would have been worth the risk."
A spokesman for the activists said another campaigner had caused a distraction outside the palace as the two men climbed on to the roof. One of the men unveiled a banner on the roof which read: "I am Harry's dad".
It is understood the Queen and Duke of Edinburgh were not at the palace during the protest.
The demonstration was part of a joint campaign by the groups New Fathers 4 Justice and Stop The War On Dads. They have called for equal rights for fathers in divorce and separation proceedings and reform of the family courts.
A third activist, James Dennis from Bishops Cleeve, Gloucestershire, also attempted to scale the roof but is thought to have failed as security arrived, the spokesman said.
Mr Matthews, from Great Bookham, Surrey, said he was "delighted" the protest had raised awareness of his cause.
Mr Smith, from Stevenage, Hertfordshire, dressed as Sesame Street character Elmo when he stood against David Cameron in the Prime Minister's constituency of Witney, Oxfordshire, in the general election. The activist also previously scaled Westminster Abbey on Father's Day.
A Metropolitan Police spokesman said officers were called to a report of a protest taking place at the Queen's Gallery at 4.28pm.
The incident ended at around 11pm and two men were arrested on suspicion of trespassing on a protected site, the spokesman said.