Extinction Rebellion has gained public support from celebrities including comedian and author Stephen Fry and Game of Thrones actor Jerome Flynn.
In a video shared on Twitter, Fry praised the group for attempting to “make politicians really recalibrate, realign, revolutionise politics” through their “mucky” and “disruptive” demonstrations.
Mr Flynn attended a protest on Sunday evening in which three activists scaled the entrance of the Guildhall building in central London.
A crowd of around 200 people gathered as the trio sprayed red spray paint over the walls of the building and unfurled a banner reading “co-liberation freedom together”.
The Game Of Thrones actor said it was “more urgent than ever” for people to take a stand together.
“We’ve gotten used to certain systems that are life destructive, we created them, we’ve become addicted to them and we know the world is burning as a result,” he said.
“It feels needed and more poignant and more urgent than ever to come together.
“It’s time to collaborate, there are so many things that are trying to polarise us and pull us apart.”
The Metropolitan Police said a total of nine people had been arrested on Sunday in connection with the activities.
The force said three had been arrested on suspicion of criminal damage and a further five were arrested for conspiracy to cause criminal damage.
One additional person was arrested for going equipped to cause criminal damage and all remain in police custody.