Famous London sites were the sites of anti-pollution activists
Activists have attached face masks to landmarks across London, breaching security around Parliament to reach a statue of Oliver Cromwell.
Two Greenpeace activists climbed the 171ft of Nelson's Column as part of a protest against the capital's "dangerous" air pollution - as others targeted statues of Eros in Piccadilly Circus, Queen Victoria, Sherlock Holmes, Thierry Henry and Sir Winston Churchill.
"Monitoring shows that, if these statutes were real people, many of them would often be breathing dangerous, illegal air," campaigner Areeba Hamid said. "That's why we've given them face masks. Of course many millions of Londoners, including kids, are breathing that same air. Kitting everyone out with face masks is not the solution; instead we need to see real political action from the new mayor. We need a clean air zone covering a large part of the city."
The Oliver Cromwell statue, which stands inside the security cordon around the Houses of Parliament, was climbed by a man and a woman in hard hats just before 6.25am.
They climbed down shortly afterwards and were met by police and arrested. Two other people were also arrested in connection with the incident.
A parliamentary spokeswoman said: "There was a minor security incident on the parliamentary estate that is being dealt with by the Metropolitan Police Service. Parliament is working closely with the police on their investigation and we cannot comment further while this is ongoing.
Greenpeace said air pollution is "cutting short 40,000 lives every year. There isn't a technological barrier stopping us from breathing cleaner air, we have the science and the tech know-how to put a stop to this crisis. What’s stopping us is lack of action from our politicians."
The campaigners want an expanded clean air zone in London.
The current proposal for an ultra-low emissions zone only offers protection for those inside zone 1 of central London from 2020.