Extinction Rebellion says supporters have superglued themselves around the Speaker’s chair in the Commons chamber.
The campaign group posted a photo on Twitter showing three members hand-in-hand in front of the seat while two other members held up signs.
One read “Let the people decide” and the other noted “Citizens’ assembly now”.
The group wrote: “Extinction Rebellion supporters have superglued around the Speaker’s chair inside the Commons chamber.
“Right now inside Parliament a speech is being read out demanding a Citizens’ assembly now: ‘We are in crisis. We can not afford to carry on like this’.”
The group also released photos showing a sign attached to scaffolding inside the parliamentary estate near Westminster Hall.
“The protest points to the need for a citizens’ assembly to cut through the corruption in Westminster, update politics & let the people decide,” they said.
Extinction Rebellion said a group of around 50 people were involved in the “non-violent” action at the Palace of Westminster.
They said three people booked on an official tour of the building and then glued themselves in a chain around the chair.
Alanna Byrne, of the group said: “It is possible to change things and update politics so it really represents ordinary people.
“Independent citizens’ assemblies can show that those blocking progress in Westminster have no democratic mandate to continue destroying the environment and give power back to people. Selected like a jury and supported with independent, expert knowledge, this is true democracy that reflects the diversity of the population.
“But to create a new, fairer politics will require first thousands, then millions of us. It will require sustained culture-shifting civil disobedience, until we become impossible to ignore. Then, when there’s enough of us, positive change will become inevitable.”