The anti-road building protests of the 1990s led to a huge increase in the cost of road building, environmentalists have claimed.
The Newbury bypass took 34 months to complete
Figures obtained under the Freedom of Information Act show that the campaign against the M11 extension contributed to a 100% increase in costs.
The Newbury bypass - the scene of Britain's most notorious road protest - was 50% over budget.
Protesters are warning of a similar campaign against airport expansion.
They say the projects ran over budget because of their action, but a spokesman for the Highways Agency said the protesters were only one factor that caused budgets to overrun.
During the M11 campaign protesters barricaded themselves inside houses in east London, which were later bulldozed.
In Newbury they dug tunnels and took to the trees.
The road cost in excess of £100m and took 34 months to complete. It was opened in November 1998.
In total more than 1,000 people were arrested.