More than 80 protesters have been arrested for an alleged attack on the power industry.
A spokesman for Nottinghamshire Police said: "Officers have this morning arrested over 80 people at a location in the Sneinton area of Nottingham on suspicion of conspiracy to commit aggravated trespass and criminal damage at a power industry facility."
Police refused to comment on the circumstances surrounding the arrests and said they would not be releasing any details until Tuesday.
It is believed the protesters were targeting the Eastcroft incinerator off Meadow Lane in Nottingham.
Jon Beresford, chairman of Nottingham Against Incineration and Landfill (NAIL), said people had become increasingly angry after the Government gave the go-ahead to a planned expansion of the plant.
He said: "Apparently the police blocked off a couple of roads and went in and made loads of arrests.
"The incinerator dominates Sneinton and since that decision there have been a lot of angry people there."
He added that he believed the people arrested may be members of a direct action group called Eastside Climate Action.