A group of campaigners from Greenpeace have climbed the Foreign Office in central London in protest.
Four demonstrators unfurled a banner as they dangled themselves on columns on the King Charles Street Archway in Westminster.
The protest centres around a treaty, which aims to protect large areas of marine life by putting stricter regulations on deep sea mining and fishing.
It was first agreed in March 2023 and has been ratified by 21 countries so far, ahead of the UN Ocean Conference in June.
Four Greenpeace activists unfurl a banner saying 'Lammy don't dally'
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Greenpeace activists who have scaled the King Charles Street Archway
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Four Greenpeace activists unfurl a banner calling for Foreign Secretary David Lammy to sign the Global Ocean Treaty into UK law
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Oceans campaigner at Greenpeace UK Erica Finnie 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."
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The protest centres around a treaty, which aims to protect large areas of marine life by putting stricter regulations on deep sea mining and fishing
PA
A Met Police spokesman told GB News: "Police were called at approximately 5.45am on Thursday, April 3 to reports of a protest at King Charles Street, SW1.
"Officers attended. Four people, three men and one woman, were safely detained and arrested on suspicion of section 1 of the Public Order Act, aggravated trespass and criminal damage.
"They have been taken to a central London police station."
GB News has approached the Foreign Office for a comment.