Crowds of people gathered in Parliament Square to hear speakers at The Big One event, which is running from 21-24 April and is expected to attract up to 50,000 people.

Many in the good-natured crowds wore fancy dress, including the distinctive red-robed army of XR protesters, while others wore masks depicting the King and Prime Minister Rishi Sunak.

The event took place on the 53rd Earth Day, an environmental event which first took place in 1970.

Wildlife presenter Chris Packham called "every last person who cares" about the planet to join XR in a passionate rallying speech.

Mr Packham said the protesters' "mission" was to "build as wide a community as possible".

He said: "Our planet is in crisis and if we don't take action then we will not protect that life, which includes us.

"One thing is clear and that is that we need to step up... We want every last person who cares to get involved, because caring is not enough."

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Just Stop Oil refuses to rule out London Marathon disruption amid weekend of protests

Following concerns that previous protests were alienating potential supporters for being too disruptive, XR made The Big One as accessible to all by not attempting to block London's streets or bridges.

Many activists attended with their children to inspire the next generation to join their ranks.

Edwina Lawson, 42, was at Parliament Square with her children and said XR's protests were "easier" for families to support than Just Stop Oil, a more radical group, but she felt such activists were "very very brave".

She told PA news agency: "Like everyone else, I'm really really concerned that the powers that be are not paying attention to the climate crisis and things are getting worse.

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"I think there's so much positive that could be done about the energy that we use, and you could create so many jobs through renewables and I think changing energy sources is the number one demand."

On Sunday, the protest will continue while tens of thousands of runners take part in the TCS London Marathon.

XR has said it has worked with TCS organisers to ensure the marathon will not be disrupted.