Plans for a 6,000-strong force to come to the aid of the civil authorities in the event of a major terrorist attack, were unveiled yesterday.

Defence Secretary Geoff Hoon said the forces' volunteer reservists could play an important role in meeting the challenges posed by international terrorism following September 11.

However, the Tories warned that Britain was already lagging behind the US in strengthening its homeland defences and said it was essential that the new force was backed by additional cash.

Under the Government's plans, set out in a consultation document, the proposed force will be drawn from the 50,700 part-time volunteer reservists of the Royal Navy, Royal Marines, Army and Royal Air Force.

The reservists will continue to serve with their normal units, but about 500 will be earmarked for the reaction force in each military region, giving a total of about 6,000.

The force would be held at a state of "graduated readiness" - with the first elements available to assist the police and other civil authorities within hours of any incident.

It would be able to help in dealing with mass casualties, mounting search and clearance operations, restoring transport and communications and operating food and water supply points.

It envisages that the new force would only be deployed in the "wholly exceptional" circumstances of a major terrorist attack.

More than one attack may be mounted at the same time in order to maximise the impact, and the terrorists may try to emulate the "massive effect" of September 11 by using weapons of mass destruction.

"Chemical, biological, radiological or even nuclear devices cannot be ruled out," the paper warned.

* FBI agents have contacted hundreds of diving equipment shops around the US, concerned that the next wave of terror attacks could come from the sea.

It is looking into whether al Qaida operatives have been taking scuba training in order to blow up ships, power plants, bridges, depots or other waterfront targets