Activists from the environmental pressure group Extinction Rebellion vowed Wednesday to challenge a blanket protest ban imposed by the London police.

Extinction Rebellion protesters demonstrate at Whitehall, London, Britain, October 8, 2019. (Photo: AFP)

The authorities told activists late Monday to leave their designated site in Trafalgar Square after a week of disruptions across the UK capital.

But pop-up actions have continued outside a few government buildings, resulting in more arrests.

Around 100 mothers with babies blockaded the entrance to Google's London office on Wednesday, alleging links to "climate change deniers". 

Elsewhere, five young activists climbed on top of the entrance to YouTube's London offices, demanding that the video-sharing site "stop platforming climate denial".

London police reported more than 1,460 arrests as of Wednesday morning. An overwhelming majority of those detained were booked and immediately released.

The group is seeking a judicial review at the High Court and an urgent hearing into police action to stop the protests and prevent disruption.

"The ban is a disproportionate and unprecedented curtailment of the right to free speech and free assembly," the Extinction Rebellion statement said.

The group is protesting what it sees as government inaction in the face of climate change.

The British government has adopted guidelines aimed at reducing polluting emissions to a net level of zero by 2050. 

But Extinction Rebellion wants all governments to hit that target by 2025.

It concedes that it has no specific proposals for how businesses and governments can radically alter their way of doing business in six years.

The group wants to set up special "citizens' assemblies", in which the mechanisms could be discussed.