The exercise was one of the largest in Britain

Nearly 900 soldiers, police officers, firefighters and paramedics took part in the simulated incident at Dalton Barracks, near Abingdon, Oxfordshire.

The Territorial Army troops involved - from the Thames Valley and Hampshire - were part of the new Civil Contingencies Reaction Force (CCRF).

Set up after the 11 September attacks, the force is designated to come under police command in the event of natural disasters, accidents or terrorist attacks.

This is possibly the biggest and certainly one of the biggest exercises of its kind to be staged in the country Army spokesman

The exercise saw those troops establishing a centre to cope with a large-scale evacuation after a "major chemical incident".

Meanwhile, fire and rescue services from Oxfordshire, Buckinghamshire and Berkshire sealed off the area and began the mock decontamination of people.

They worked closely with police, the ambulance service and local council representatives in the exercise, codenamed Autumn Roebuck 2.

About 400 soldiers and cadets acted as civilians while 200 soldiers, 150 firefighters with 30 appliances and 60 police officers took part.

Mr Searle was pleased with how the exercise went

Captain Marcus Dicks, of the Royal Rifles Volunteers, said: "We have to remember we would be dealing with civilians here, not soldiers.

"They would be shocked, tired, hungry and cold and it would be up to us to look after them at the same time as processing them through the centre."

Richard Searle, emergency planning officer at Thames Valley Police, said: "It has gone well today considering it is the first time we have worked together with the CCRF."

The exercise comes after a simulated terrorist attack on the Tube was held in London in September.