Oscar-winner Emma Thompson rallies London climate campaigners

Thompson climbed onto a pink boat at Oxford Circus and addressed crowds on Good Friday as the campaign group declared a separate protest at Heathrow Airport was over.

"We are here in this little island of sanity and it makes me so happy to be able to join you all and to add my voice to the young people here who have inspired a whole new movement," she said to cheers of support.

Speaking to reporters, she said her generation had failed to protect the planet for young people.

Thompson, who also joined demonstrators on Thursday, added: "We have seriously failed them and our planet is in serious trouble, we have much, much less time than we thought.

"I have seen the evidence for myself and I really care about my children and grandchildren enough to want to be here today to stand with the next generation."

The Love Actually actress also challenged critics who have said demonstrators are using the protests to have fun.

"If you can't have fun whilst saving the planet, what's the point?" she asked.

"Protest should always have a sense of joy in it because what we are protesting about is saving this extraordinary home of ours and also celebrating the passion and inspiring energy of this young generation.

"These are young people who have finally said to my generation 'I'm so sorry but you have failed us'.

"We all feel dreadful about that. My feeling is I feel massively inspired by this young generation and want to stand next to them."

She said climate change is "the most pressing and urgent problem of our time, in the history of the human race".

Shortly after Dame Emma's address, a team of police officers encircled the boat and told bystanders there was an ordinance to clear the area.

Earlier, on Friday morning, about 20 activists, most of them under 17, had staged a brief demonstration on roads near Heathrow Airport.

Standing close to a tunnel which leads to terminals two and three, they unfurled a black banner with the message: "Are we the last generation?"

Several police officers watched over group before an XR spokesman announced before midday there were no further plans to cause disruption at the airport.

All roads remained open during the demonstration, which is part of a two-week campaign that began in central London on Monday.

Heathrow previously said it was "working with authorities" to remain business as usual.

Waterloo Bridge has now been blocked by demonstrators for five days despite the Metropolitan Police making more than 570 arrests.

Ten people had been charged by the force by Thursday night and three others arrested by British Transport Police were remanded in custody after they appeared in court accused of obstructing trains at Canary Wharf.

The Met said: "The protesters are using tactics of lying on the ground when approached. This means that it takes at least four officers to remove one person to ensure their safety which is resource intensive."

Routes are also blocked around Parliament Square and Marble Arch, and Home Secretary Sajid Javid has urged police to use the "full force of the law".

"I totally condemn any protesters who are stepping outside the boundaries of the law," Javid said.

"They have no right to cause misery for the millions of people who are trying to lead their daily lives."

Ken Marsh, chairman of the Metropolitan Police Federation, told BBC Breakfast the protests were "very, very difficult" to handle and could cost "millions".

He said: "The sufferers will be the communities in the local boroughs where officers are being taken from the community areas and the funding and money has to be found to deal with what we are doing."

XR has pledged to continue causing disruption until its demands are met.

They want the Government to declare a climate emergency and take action to reduce greenhouse gas emissions to net zero by 2025.