The head of North Yorkshire Police has defended the decision to draft in hundreds of officers from across the country to police Drax power station.
Officers from seven forces were drafted in to help the operation
Chief Constable Della Cannings said the cost of Operation Harmony to the North Yorkshire force would be "substantial" but said it had been a success.
Seven forces were drafted in to stop protesters shutting down Britain's biggest coal-fired power station.
A total of 38 people were arrested during the demonstration.
Officers had believed there would be up to 2,000 protestors trying to close down the site on the organised day of "creative mass action" but 600 were thought to have turned up.
Mrs Cannings said: "We were in a no-win situation.
"If nothing much happened people would say we were over-policing, but if there had been an incursion to the power station they would have said it was under-policed."
The police chief said the total cost of the operation would be reported to the police authority in the future.
"It's obviously a substantial cost, we can't deny that", she said.
"But the police authority has been very prudent and has a contingency fund for things like major murder inquiries and operations like this."