Policing Just Stop Oil protests cost the Metropolitan Police £7.5m in nine weeks, it has been revealed.
Environmental activists caused huge disruption in London last autumn when demonstrators blocked traffic on busy motorways and main roads.
The cost, revealed in a Freedom of Information request, includes the cost of staffing, overtime and vehicle use.
Home Secretary Suella Braverman says "enough is enough" and claimed the protests "drained police resources".
The group wants the government to halt new licences for the exploration of oil and other fossil fuels in the UK.
More than 13,600 police officer shifts were involved in responding to incidents from 1 October to 14 November and from 28 November to 14 December.
Ms Braverman said: "Enough is enough. Blocking motorways and slow walking in roads delays our life-saving emergency services, stops people getting to work and drains police resources."
"Everyone has the right to protest but some of their activity was not protest, this was outright criminality intent on disrupting London, which we had to respond to effectively," she said.
Force bosses said because Just Stop Oil had not engaged with them in planning protests they had to have staff ready at all times.
Just Stop Oil spokesman Grahame Buss described the cost of policing the group's actions as "proportionate" given the billions of pounds being spent globally "adapting to climate change".
He added: "People are already dying because of the climate crisis. It really is a very serious issue.
"Overall, the costs of averting it are far less than the cost of ignoring it."
The government is attempting to tighten laws around protests through a Public Order Bill.
Ministers suffered a series of defeats on the legislation in the House of Lords this week, and peers will vote on an amendment on serious disruption on Tuesday.