The Just Stop Oil (JSO) group said two of its supporters spray-painted with chalk "1.5 is dead" on the 19th-century biologist's grave in Westminster Abbey in central London.

It follows Europe's climate monitor last week announcing that the last two years saw average global temperatures exceed the critical 1.5C warming limit for the first time.

London's Metropolitan Police said that officers arrested two women on suspicion of causing criminal damage "with what is believed to be powdered paint at Westminster Abbey".

"Police were called... following reports that the women had been detained by security," a spokesman said.

"They have been taken to a central London police station where they remain in custody."

A spokesperson for the church said it did not anticipate permanent damage and its doors remained open for worshippers and visitors.

JSO, formed in early 2022 to pressure the UK government over oil and gas exploration policy, named the two activists behind the stunt.

It said Alyson Lee, 66, a retired teaching assistant, and Di Bligh, a 77-year-old former chief executive of a local government council, were involved.

"We are trying to get the government to act on climate change. They are not doing enough," Lee told reporters as she was led away by police.

JSO have carried out a spate of such stunts, including targeting iconic paintings like Vincent van Gogh's "Sunflowers" with soup and the megalithic standing stones at Stonehenge with orange paint powder.