Four climate change activists have been arrested after scaling the gates of Buckingham Palace and chaining themselves to the railings.

Three men and one woman who said they represented the Climate Siren group locked themselves to the centre gate and south centre gate just after 2pm today, wearing t-shirts bearing the words "climate emergency. 10% annual emission cuts," and wielding megaphones.

Two of them held a banner carrying a quote from the Prince of Wales reading: "The doomsday clock of climate change is ticking ever faster towards midnight. We are simply not reacting quickly enough."

The four were removed by police using a cherry-picker more than four hours later as officers brought the protest to an end.

They were detained on suspicion of breaching Royal Parks regulations.

A Metropolitan Police spokesman said:

"At approximately 2.05pm on Saturday June 23, four protesters - three men and one woman - climbed the centre gate and south centre gate at Buckingham Palace and secured themselves to the railings with chains. "Police attended and by around 6.35pm all the protesters had been removed and arrested under SOCPA (the Serious Organised Crime and Police Act) and for breaching section 4 of the Royal Parks and Other Open Spaces Regulations 1997. "They have been taken to various central London police stations where they remain in custody."

A handful of other Climate Siren activists carrying banners were also on the scene.

Taking action the day after the Rio+20 global conference on sustainable development in Rio de Janeiro, Brazil, came to a close, the group said they were calling on the Queen to follow her son's example in speaking out about "the escalating threat of catastrophic climate change".

A hundred or so bystanders stood and watched the protest.

Charles issued his warning that action on climate change was not being taken quickly enough in a speech to the European Parliament in Brussels in February 2008.