Climate change protesters ended a 24-hour rooftop protest at Britain's Houses of Parliament late Monday, as authorities launched an "urgent" investigation into how they scaled the landmark.

Around 50 Greenpeace activists spent Sunday night on top of the Palace of Westminster to urge lawmakers returning from their summer break to take action to cut carbon emissions before the UN's key Copenhagen summit in December.

Police said all the remaining protesters had come down from the roof and 19 were arrested, while 23 activists detained overnight Sunday have been bailed.

The demonstrators had unfurled yellow banners which read: "Change the politics, save the climate".

Greenpeace's executive director John Sauven said the demonstration had been "an amazing success".

"With our MPs back from the summer break and the UN climate conference in Copenhagen just around the corner, it's time to see some real leadership from our elected politicians," he added.

"They need to make climate change, green jobs and a low carbon economy their top priorities rather than obsessing over their short-term prospects at the next election.

"We're at one minute to midnight, and the clock is ticking."

House of Commons Speaker John Bercow told the first parliamentary session after a three-month break that the security breach would be investigated with immediate effect.

"We do not discuss matters of security in this chamber but I wanted to say to the house that I have had a preliminary report and the full circumstances are now being investigated urgently and thoroughly," Bercow said.

"Whatever action is necessary will be taken."

It was not the first security lapse at the parliament in recent years.

In March 2004, Greenpeace demonstrators scaled the landmark clock tower on the first anniversary of the invasion of Iraq.

Two months later, fathers' rights campaigners threw condoms of purple flour in the House of Commons, hitting then-prime minister Tony Blair.

The same year, five protesters burst into the chamber to protest during a hunting ban debate, and protesters also got onto the roof in February 2008 to demonstrate against a planned third runway at London's Heathrow airport.

The December 7-18 United Nations climate summit in Copenhagen will see nations attempt to draw up a new global climate treaty to replace the Kyoto Protocol which expires in 2012.

earlier related report
Environment activists occupy British parliament roof
Environmental campaigners were occupying the roof of Britain's parliament Monday in a bid to urge returning lawmakers to overhaul their climate change policies before the UN's key Copenhagen summit.

Around 30 Greenpeace activists evaded security Sunday and clambered onto the roof of the famous Palace of Westminster in central London, unfurling several yellow banners reading: "Change the politics, save the climate".

The demonstrators waited through the night for Monday morning, when lawmakers return from their summer break, to urge them to sign up to a 12-point manifesto.

"We've got to raise the temperature of the debate because we are really running out of time," said Greenpeace executive director John Sauven.

"Parliament is opening and there is an election looming so this is a golden opportunity for the political parties to really think about the future."

Speaking from the roof, Greenpeace employee Brikesh Singh, 29, from Bangalore in southern India, said the protesters had energy bars and warm clothing to get them through the night.

"This building is considered as the mother of all parliaments and the UK is one of the leading developed countries," the demonstrator said.

"We want them (lawmakers) to get the message loud and clear that if you want a planet-saving deal in Copenhagen we need to change the climate policy."

The December 7-18 United Nations climate summit in Copenhagen will see nations attempt to hammer out a new global climate treaty to replace the Kyoto Protocol which expires in 2012.

A spokesman for London's Metropolitan Police said: "Approximately thirty protestors remain on the roof of the Houses of Parliament.

"The intention of the police is to bring the protestors down off of the roof safely.

"Officers are talking with a representative of the protestors on the ground. All peaceful."

A spokeswoman from the Department for Energy and Climate Change said activism on the subject was welcome but had to respect the law.

"We have a comprehensive plan to transform our economy and society, by investing in green jobs, cleaning up our energy supplies and making our homes energy efficient," she said.

"This week we host vital talks to accelerate the development of clean coal and to progress the Copenhagen deal. It's our domestic record that has given us the credibility we need to press hard for an ambitious global climate deal."

It is not the first breach of security in recent times at the palace.

In March 2004, Greenpeace demonstrators scaled the landmark clock tower on the first anniversary of the invasion of Iraq.

Two months later, fathers' rights campaigners threw condoms full of purple flour in the lower House of Commons, hitting then-prime minister Tony Blair.

Four months on, five protesters got into the chamber to protest during a hunting ban debate.

And protesters got onto the roof in February 2008 to demonstrate against a planned third runway at London's Heathrow airport.