A group of largely-naked Extinction Rebellion protesters with messages painted on their bodies stood up in the public gallery overlooking the debate on Monday night.
Some were pressed against the glass which separates the gallery from the chamber, with police who were sent to the scene to negotiate saying one had “super-glued” themselves to the window.
MPs were seen taking a glance up at the protest and Speaker John Bercow maintained that the debate on the second stage of the Brexit alternatives would proceed despite the protest.
Scotland Yard said: “12 arrests have been made for outraging public decency.”
An earlier statement from the force had said: “The protesters are naked and one of them has super-glued themselves to a window.
“Officers are on scene and attempting to negotiate with them.”
Extinction Rebellion, which describes itself as a non-violent direct action and civil disobedience group, said the protest was an attempt to draw politicians’ attentions to the “climate and ecological crisis”.
Protester Savannah, an English literature student from Ladbroke Grove, told the Press Association: “Everyone stripped and two people were elephants and had climate crisis written on them.
“We were pointing at them as the elephants in the room of the Brexit debate.”
She added: “Personally I don’t care that much about Brexit.
“I think it’s fine that people do but I think there are bigger things right now.”
The group of men and women with slogans stood up as Labour MP Peter Kyle was making a speech.
One of the MPs speaking during the nude protest, Tory Nick Boles, made a joke that his Brexiteer colleagues were “noted naturists”.
“It has long been a thoroughly British trait to be able to ignore pointless nakedness, and I trust the House will be able to return to the issue that we are discussing,” he added.
An Extinction Rebellion spokesman said the naked protest was an effort “to try and force the issue up the news agenda as far as possible so it breaks through the Brexit Radar”.
“They have gone in there knowing they will be arrested. They are willingly doing this,” he added.
Several doorkeepers attempted to remove the protesters, but they remained in position for several minutes.
The dozen or so semi-naked protesters stood in a line with their backs pressed against the security glass of the public gallery. Most were only wearing knickers or underpants.
On their bodies were written the words “Climate justice act now” and “eco collapse”.