More than £7m was spent on policing during the climate change protest at Heathrow Airport, Scotland Yard says.
There were some minor skirmishes between police and protesters
Up to 1,800 police officers were on duty on busy days during the eight-day Camp for Climate Action last month.
Some 70 people were arrested as protesters demonstrated against the airport's expansion, the Metropolitan Police Authority (MPA) was told.
Commander Bob Broadhurst said £4.3m would have been spent anyway, as it included bills such as salaries.
The protest culminated with a blockade by hundreds of anti-aviation campaigners of the offices of airport operator BAA on 19 August.
The final day of action was marked by a series of demonstrations at businesses across the UK.
Sizewell B nuclear power station in Suffolk, the headquarters of BP in London and two carbon offsetting companies were singled out.