Climate change protesters in London have been warned they risk a large fine if they fail to comply with coronavirus rules banning gatherings of more than 30 people.

The Met Police said risk assessments explaining how Extinction Rebellion (XR) activists were minimising the possibility of Covid-19 transmission “did not meet the required standard”.

The force said XR’s latest round of demonstrations “pose a risk, not only to those involved, but to the wider public and communities of London”.

Last Sunday, former Labour leader Jeremy Corbyn’s brother Piers was fined £10,000 for arranging a protest in Trafalgar Square involving hundreds of anti-mask and anti-vaccination activists.

In an open letter to XR protesters on Friday, the Met said: “It is your responsibility to check the position and ensure you are not committing an offence by being involved in a large gathering.

“We urge anyone arranging a gathering to inform your local police. We all need to continue to do our part to prevent the spread of the virus.”

The climate action, which began on September 1, has so far seen more than 500 arrests.

About 200 of those were linked to a blockade of Lambeth Bridge on Thursday, which shut the route off to traffic.

Earlier in the day, protesters glued themselves to the ground around Parliament, while others staged sit-ins at other entrances to the parliamentary estate.

Friday was a quieter day, but on Saturday a procession of activists that set of from Brighton on foot a week ago is due to march the final stretch to Parliament.

They have been banned from taking a 20ft model boat named after teenage activist Greta Thunberg to the streets of Westminster.

On Friday Met Police Assistant Commissioner Louisa Rolf warned the group not to take The Lightship Greta into an area stretching from Green Park to Lambeth.

She imposed an order under Section 12(3) of the Public Order Act 1986, saying: “I reasonably believe that the procession may result in serious disruption to the life of the community.”

The Lightship Greta features the words “Sound the alarm – Climate Emergency” on its side.

Claudia Fisher, 58, of Extinction Rebellion Brighton, said of the boat: “The voyage of Lightship Greta aims to highlight the journey that many climate refugees are taking right now and many millions more will be forced to undertake.

“More of us will be displaced and have to leave our homes for each degree of heating of our earth.

“As the seawater rises and the fires burn, where would you go? This is a crisis that will impact us all – it is just a matter of time, and time is running out.”