A squad of 12 police officers dressed in combat gear raided a flat in a peaceful street yesterday as part of a joint police-army operation.

They startled neighbours as they leapt from two vehicles in a nearby factory yard and marched to the ground floor apartment in Queen Street, Barnard Castle, Co Durham.

The squad was made up of officers from the County Durham force and the Ministry of Defence police force based at Catterick Garrison, North Yorks. Their joint raid was planned amid tight security.

An MoD police spokesman said later, "We have arrested a 48 year old man, but we can't say any more at this stage. We are unable to say what we were searching for. The officers who made the raid were not armed."

He said the MoD police wear uniforms like those of civilian police and are a different unit to the Royal Military Police, known as Redcaps.

The tenant of the flat is understood to be a former soldier who has recently been working with an army cadet force unit. He was in the flat when it was raided.

The officers carried a large aluminium box and ladder as they went into the building, converted from an old police station and magistrates' courts.

One woman who saw the raid shortly before 8am said, "It was really dramatic and a bit frightening. A few officers went in first and then the others marched down the road like a military squad."

Another woman stated, "It looked as if it must be a very serious incident. You don't expect a lot of police to rush about in a quiet area like this."

The two large police vehicles were parked in the yard of Smiths' sign making factory. Policemen went to and from them several times during the search.

The building was the town's main police station for many years, and two of the upstairs rooms were used as courts. After the police moved out to a new station the magistrates continued to hold sessions there.

After the courts closed the building stood empty for some years before the Three Rivers Housing Association took it over and converted it into flats three years ago.