Some 15 Just Stop Oil protesters have been arrested while blocking traffic and slow-marching on Whitehall in central London.
Metropolitan Police officers cleared the area within five minutes and traffic is now flowing freely.
The arrests were made under Section Seven of the Public Order Act, which says a protester can be taken in if they "intentionally or recklessly interfere with the use or operation of any key national infrastructure" or "disproportionately interferes with road transport infrastructure".
Officers are supposed to take into account a person's right to protest before taking them into custody.
Just Stop Oil said it would be staging daily marches from Trafalgar Square from November 20 in its bid to get the Government to end new oil and gas licences.
The Met has made nearly 500 arrests of eco-activists associated with the group since October 30, with more than 200 charges.
On Saturday, an 18-year-old man was arrested before a Just Stop Oil march began - for breaking bail conditions set by a court by being in London.
This was the second time he had been arrested that week.
At the time, demonstrator Pippa Cowtan, 21, a politics graduate who joined the march on the weekend, said: “The Government cannot arrest its way out of the situation we are in, just like we cannot vote our way out.
“I am taking action because I cannot sit back and be complicit in the government's plans to let millions die, so they can further line their pockets.
“We have to come together to resist, because together we can be the opposition the country needs, and we can win.”
The group has not yet commented on Monday's action, but it posted an article about "the world's richest 1 per cent causing more carbon emissions than the poorest 66 per cent" earlier in the day.
The activists wrote: "Is this really news? In the UK we have a billionaire PM who travels by private jet and wants to license 100+ new oil and gas projects for his mates — while everyone else tries to recycle their oat milk cartons. "
