London: British Prime Minister Tony Blair has announced plans for a new multibillion-dollar submarine-based nuclear deterrent but said the Government would cut the number of nuclear warheads by 20 per cent.

Declaring that it would be unwise and dangerous for UK to give up its nuclear weapons, Blair laid out plans yesterday to spend up to 20 billion pounds on a new generation of nuclear submarines for Trident missiles.

In a move to placate critics in the Labour Party, Blair announced in the House of Commons that Britain's stockpile of nuclear warheads would be cut by a fifth from around 200 to fewer than 160.

The Government's White Paper formally ratified at a special meeting of the Cabinet - also left open the option of reducing the submarine fleet from four to three.

Blair said that although the Cold War had ended the UK needed nuclear weapons as no-one could be sure another nuclear threat would not emerge in the future.

He said the options of changing to a land-based, or air-based nuclear weapons system had been considered and ruled out.

Instead the system would remain one based on a fleet of submarines which carry the Trident missiles, each of which can be fitted with a number of nuclear warheads.

Blair said between 15 billion pounds and 20 billion pounds would be spent on the new submarines to carry the Trident missiles. The submarines would take 17 years to develop and build, and would last until about 2050.

He said the UK would also join the US programme to extend the life of the Trident missiles until 2042 and would then work with the US on successor missiles.