Greenpeace activists have scaled a building outside the Foreign Office in protest over delays to signing an international treaty protecting oceans.
Four protesters unfurled a banner as they suspended themselves on columns on the King Charles Street Archway in Westminster early on Thursday morning.
The group called for faster action from Foreign Secretary David Lammy in signing the Global Ocean Treaty, with the banner showing a turtle with the words "Lammy don't dally!".
The treaty, which aims to protect large areas of marine life by putting stricter regulations on deep sea mining and fishing, was first agreed in March 2023 and has been ratified by 21 countries so far, ahead of the United Nations Ocean Conference in June.
Mr Lammy was in Brussels for a meeting of Nato foreign ministers on Thursday.
Erica Finnie, oceans campaigner at Greenpeace UK, said: "The ocean is home to so many spectacular marine creatures, but sadly David Lammy has taken inspiration from the sea snail to pass the Global Ocean Treaty into UK law.
"The Foreign Secretary and his staff love to talk about the importance of nature and ocean protection, yet this historic global agreement appears to be floundering.
"So we stopped by his office to deliver a message: stop dallying and get your flippers on.
"Unless the Government lifts the anchor fast, it risks the embarrassment of not being able to shape key decisions at the first 'conference of the parties' of the treaty."
The Metropolitan Police said it was called to reports of a protest at King Charles Street at around 5.45am on Thursday, and that the road remains closed.
Emergency services including the police and fire brigade were in attendance at the scene, with a small cordon formed around the archway.
Whitehall remained open to traffic.
