Activists poured hundreds of litres of fake blood into the road outside Downing Street to demand action on climate change.

Police stood by watching, without making any arrests, as protesters simultaneously tipped up buckets of the red liquid, which spread across the breadth of the road.

An estimated 400 demonstrators from the groups Extinction Rebellion and Christian Climate Action staged the protest, simulating a “sea of blood”.

They said pouring the liquid, which they dubbed “the Blood of our Children”, symbolised the “gravity” of the ecology and climate emergency.

The groups said they were prepared to risk arrest as part of a mass civil disobedience movement to force those in power to act.

So far, governments worldwide have failed to take sufficient meaningful action, they believe.

Extinction rebellion: Climate change protesters block London bridges Show all 25 1 /25 Extinction rebellion: Climate change protesters block London bridges Extinction rebellion: Climate change protesters block London bridges Demonstrators block Westminster Bridge in central London to show anger at government inaction on climate and ecological issues AFP/Getty Extinction rebellion: Climate change protesters block London bridges A pro environment protester is arrested by police on Lambeth bridge in London EPA Extinction rebellion: Climate change protesters block London bridges Organised by Extinction Rebellion, the protest is part of many taking place this weekend to bring attention to political inaction on issues of pollution and climate change Reuters Extinction rebellion: Climate change protesters block London bridges A demonstrator puts tape on her mouth as she takes part in a pro-environment protest blocking Westminster Bridge in central London on November 17, 2018, calling on the British government to take action on climate and ecological issues. - Organized by Extinction Rebellion, the protest is part of many taking place this weekend to call for action on what they describe as a climate and ecological emergency. Extinction Rebellion demands that the UK government reduces to net zero greenhouse gas emissions by 2025 and creates a citizens assembly to oversee changes in environmental policies. (Photo by Tolga AKMEN / AFP)TOLGA AKMEN/AFP/Getty Images TOLGA AKMEN AFP/Getty Extinction rebellion: Climate change protesters block London bridges Organised by Extinction Rebellion, the protest is part of many taking place this weekend to bring attention to political inaction on issues of pollution and climate change PA Extinction rebellion: Climate change protesters block London bridges Demonstrators on Blackfriars Bridge PA Extinction rebellion: Climate change protesters block London bridges Police with demonstrators on Blackfriars Bridge PA Extinction rebellion: Climate change protesters block London bridges Demonstrators take part in a pro-environment protest as they block Westminster Bridge in central London on November 17, 2018, calling on the British government to take action on climate and ecological issues. - Organized by Extinction Rebellion, the protest is part of many taking place this weekend to call for action on what they describe as a climate and ecological emergency. Extinction Rebellion demands that the UK government reduces to net zero greenhouse gas emissions by 2025 and creates a citizens assembly to oversee changes in environmental policies. (Photo by Tolga AKMEN / AFP)TOLGA AKMEN/AFP/Getty Images TOLGA AKMEN AFP/Getty Extinction rebellion: Climate change protesters block London bridges epa07172610 Pro environment protesters block Westminster bridge in central London, Britain, 17 November 2018. Reports state that the protest organized by Extinction Rebellion group is planning to close five main bridges across the river Thames, seeking to bring attention to political inaction on issues of pollution and climate change. EPA/FACUNDO ARRIZABALAGA FACUNDO ARRIZABALAGA EPA Extinction rebellion: Climate change protesters block London bridges A demonstrator is led away by police on Blackfriars Bridge PA Extinction rebellion: Climate change protesters block London bridges Environmental campaigners from the direct action group Rebellion demonstrate on Westminster Bridge in central London, Britain, November 17, 2018. REUTERS/Peter Nicholls PETER NICHOLLS Reuters Extinction rebellion: Climate change protesters block London bridges Police with demonstrators on Westminster Bridge in London for a protest called by Extinction Rebellion to raise awareness of the dangers posed by climate change. PRESS ASSOCIATION Photo. Picture date: Saturday November 17, 2018. See PA story PROTEST Rebellion. Photo credit should read: John Stillwell/PA Wire John Stillwell PA Extinction rebellion: Climate change protesters block London bridges Environmental campaigners from the direct action group Rebellion demonstrate on Westminster Bridge in central London, Britain, November 17, 2018. REUTERS/Peter Nicholls PETER NICHOLLS Reuters Extinction rebellion: Climate change protesters block London bridges Demonstrators take part in a pro-environment protest as they block Westminster Bridge, near the Houses of Parliament in central London on November 17, 2018, to show anger at government inaction on climate and ecological issues. - Organised by Extinction Rebellion, the protest is part of many taking place this weekend to bring attention to political inaction on issues of pollution and climate change. (Photo by Tolga AKMEN / AFP)TOLGA AKMEN/AFP/Getty Images TOLGA AKMEN AFP/Getty Extinction rebellion: Climate change protesters block London bridges Demonstrators take part in a pro-environment protest as they block Westminster Bridge in central London on November 17, 2018, to show anger at government inaction on climate and ecological issues. - Organized by Extinction Rebellion, the protest is part of many taking place this weekend to bring attention to political inaction on issues of pollution and climate change. (Photo by Tolga AKMEN / AFP)TOLGA AKMEN/AFP/Getty Images TOLGA AKMEN AFP/Getty Extinction rebellion: Climate change protesters block London bridges Police with demonstrators on Westminster Bridge in London for a protest called by Extinction Rebellion to raise awareness of the dangers posed by climate change. PRESS ASSOCIATION Photo. Picture date: Saturday November 17, 2018. See PA story PROTEST Rebellion. Photo credit should read: John Stillwell/PA Wire John Stillwell PA Extinction rebellion: Climate change protesters block London bridges epa07173093 A pro environment protester infornt of police on Lambeth bridge in London, Britain, 17 November 2018. Reports state that the protest organized by Extinction Rebellion group is planning to close five main bridges across the river Thames, seeking to bring attention to political inaction on issues of pollution and climate change. EPA/FACUNDO ARRIZABALAGA FACUNDO ARRIZABALAGA EPA Extinction rebellion: Climate change protesters block London bridges epa07172601 Pro environment protesters block Westminster bridge in central London, Britain, 17 November 2018. Reports state that the protest organized by Extinction Rebellion group is planning to close five main bridges across the river Thames, seeking to bring attention to political inaction on issues of pollution and climate change. EPA/FACUNDO ARRIZABALAGA FACUNDO ARRIZABALAGA EPA Extinction rebellion: Climate change protesters block London bridges epa07172698 Pro environment protesters hold a placard as they block Westminster bridge in central London, Britain, 17 November 2018. Reports state that the protest organized by Extinction Rebellion group is planning to close five main bridges across the river Thames, seeking to bring attention to political inaction on issues of pollution and climate change. EPA/FACUNDO ARRIZABALAGA FACUNDO ARRIZABALAGA EPA Extinction rebellion: Climate change protesters block London bridges Demonstrators on Westminster Bridge in London for a protest called by Extinction Rebellion to raise awareness of the dangers posed by climate change. PRESS ASSOCIATION Photo. Picture date: Saturday November 17, 2018. See PA story PROTEST Rebellion. Photo credit should read: John Stillwell/PA Wire John Stillwell PA Extinction rebellion: Climate change protesters block London bridges Environmental campaigners from the direct action group Rebellion demonstrate on Westminster Bridge in central London, Britain, November 17, 2018. REUTERS/Peter Nicholls PETER NICHOLLS Reuters Extinction rebellion: Climate change protesters block London bridges epa07172703 Pro environment protesters hold a placard as they block Westminster bridge in central London, Britain, 17 November 2018. Reports state that the protest organized by Extinction Rebellion group is planning to close five main bridges across the river Thames, seeking to bring attention to political inaction on issues of pollution and climate change. EPA/FACUNDO ARRIZABALAGA FACUNDO ARRIZABALAGA EPA Extinction rebellion: Climate change protesters block London bridges Demonstrators take part in a pro-environment protest as they block Westminster Bridge in central London on November 17, 2018, to show anger at government inaction on climate and ecological issues. - Organized by Extinction Rebellion, the protest is part of many taking place this weekend to bring attention to political inaction on issues of pollution and climate change. (Photo by Tolga AKMEN / AFP)TOLGA AKMEN/AFP/Getty Images TOLGA AKMEN AFP/Getty Extinction rebellion: Climate change protesters block London bridges epa07172629 Pro environment protester holds a placard as they block Westminster bridge in central London, Britain, 17 November 2018. Reports state that the protest organized by Extinction Rebellion group is planning to close five main bridges across the river Thames, seeking to bring attention to political inaction on issues of pollution and climate change. EPA/FACUNDO ARRIZABALAGA FACUNDO ARRIZABALAGA EPA Extinction rebellion: Climate change protesters block London bridges Environmental campaigners from the direct action group Rebellion demonstrate on Westminster Bridge in central London, Britain, November 17, 2018. REUTERS/Peter Nicholls PETER NICHOLLS Reuters

Scotland Yard said the policing was appropriate but would not comment while the event was still happening.

Protests were also held in other towns across the UK. In Colchester there was a “funeral march” and “lie-down” to mourn species extinctions.

In Scotland last night, police arrested 13 Extinction Rebellion activists who were among a group staging a protest outside an oil industry dinner at the National Museum of Scotland in Edinburgh.

They unfurled a banner reading: “Thank you for our suicide. Enjoy the feast while you still can.”

Police said those arrested were among a group who refused to leave.

An “International Rebellion” series of actions is planned in capital cities around the world from 15 April, to demand governments curb carbon dioxide emissions, limit global temperature rises and prevent mass species die-offs.

The London demonstrators called on ministers to pay as much attention to climate change as to Brexit.

“This is the biggest issue that any civilisation has ever faced. The idea that this is not the first priority of every single person and every single government is laughable,” said Teddy, Woolnough, 19.

“The climate crisis is killing people now. In London, thousands of people are dying as a result of air pollution,” said Amy Jarvis, 22.

“And on the other side of the world the situation is even worse. We are complicit in a system that is sending people to their death.”

Another activist, Jayne Forbes, said: “There are no words to describe the horrors we risk if we do not make governments act immediately. Every parent, every adult, everyone has a responsibility and duty to take action. That now means breaking the law.”