Animal Rebellion protesters have scaled up the side of the Defra building in the hope of pushing world leaders into addressing carbon emissions from farming and fishing at COP26.
The climate change protesters, part of an offshoot group of Extinction Rebellion, started climbing up a structure on the side of the Home Office, in Marsham Street, Westminster, which houses the Department for Environment, Food and Rural Affairs (Defra), at about 6am on Tuesday.
It took them about two-and-a-half hours to reach the top where they unfurled a large orange banner calling on world leaders attending the COP26 climate talks next week to "invest in a plant-based future".
Just before 9am, a police officer spoke to the protesters through a megaphone and told them to come down as they were preventing workers from entering the building.
Inspector Richards said they were trespassing with the purpose of "intimidating, obstructing and disrupting" and directed them to come down and if they failed to do so they could be arrested.
He added that they are banned from the land for three months.
A few hours later, police abseiled down from the top of the building and took down the banner but the protesters remain up there and have set up hammocks to lie in as well as letting off red flares.
One protester told Sky News: "Ahead of COP26, we are calling for - no, demanding - that the world wake up and switch to a fully plant-based diet.
"We don't do this because we want to do it, we do this because we have to do it.
"If we don't do this the government won't address it."
A leaflet protesters were handing out said the meat and dairy industries are some of the leading producers of greenhouse gases while fishing is "destroying our ocean ecosystems, contributing to dead zones and increasing acidification".
It said world leaders at COP26, due to start on Sunday in Glasgow, "cannot talk about meeting the Paris climate targets and securing net-zero emissions without addressing that our food system is destroying the planet".
The group is also asking the government to "defund meat, dairy and fishing" and invest in a "just plant-based food system".
Police, the fire brigade and London Ambulance Service were on the scene not long after the protesters started climbing but no arrests have been made.
A Met Police spokesman told Sky News: "Police were called at 06:09hrs on Tuesday, 26 October following reports that a number of protesters had scaled a government building in Marsham Street SW1.
"Officers are on scene with the London Fire Brigade. There have been no arrests at this time."