Scantily-clad demonstrators were removed from the House of Commons after they launched a protest over climate change during a debate on Brexit.
Interrupting parliamentary proceedings ahead of another crunch vote on Europe, the men and women stripped off to reveal slogans such as “Climate Justice Act Now” on their torsos.
The Metropolitan Police said 12 people were arrested for outraging public decency.
Campaign group Extinction Rebellion, which claimed responsibility for the stunt, said two of those protesting wore full grey body paint and elephant masks.
It said the demonstrators aimed “to bring the message that politicians neglect of the climate crisis has become an ‘elephant in the room’”.
James Heappey, MP for Wells, Somerset, said the incident meant parliament “just got a little bit more nuts” as those involved stripped down in the public gallery.
Several doorkeepers attempted to remove the protesters but they remained in position for several minutes before being removed by officials.
HuffPost UK’s deputy political editor, Arj Singh, said the demonstrators appeared to have glued their hands to the glass partition separating the public gallery and the Commons chamber.
Speaker John Bercow told MPs to ignore the demonstration and continue with the debate on Brexit.
Tory MP Nick Boles said ignoring “pointless” nakedness was a “British trait”.
And former Labour leader Ed Miliband was caught glancing at the demonstrators.
MPs will on Monday vote on a second round of so-called “indicative” votes on alternatives to Theresa May’s Brexit deal.
It is widely expected the option most likely to get a Commons majority is for a customs union - a much softer Brexit than the one offered by the prime minister.
While the result of the vote is not binding on the government, the PM will come under intense political pressure to adopt whatever parliament decides.