FORMER probation offices were raided by police yesterday as part of an ongoing operation in Middlesbrough.

Officers wearing gas masks and chemical suit-type coveralls searched the service's former base, in Longlands, which has been derelict for two years.

The building, in Douglas Street, was closed off as a Cleveland Police helicopter hovered overhead.

Police sniffer dogs were also sent into the building to search for evidence.

A police spokesman said the swoop was part of an ongoing clampdown on serious crime - Operation Sabre.

Scores of residents watched police in gas masks and dozens of other officers taking part in the raid.

Three men were arrested at the site.

With more raids expected in the town, a force spokeswoman last night said there would be no official comment on the exact nature of the raids until today.

Asked why officers had been masked and wearing overalls, the spokeswoman said "Because there was a suspected drugs activity, and the building was supposed to have been unoccupied for two years. We didn't know what we were going into. We have made a number of arrests.''

A plastic inflatable shelter believed to be used to spray people for decontamination was at the scene.

Police sniffer dogs searched a lock-up garage in Douglas Street, near the back of the Baltimore Hotel.

The spokeswoman declined to say whether narcotics or drugs paraphernalia were recovered from the building.

She categorically denied a report that armed officers were used in the raids.

Police officers were seen to erect a tent at the premises in Douglas Street, which will be the subject of a detailed examination by forensic experts today.