Labour and the Liberal Democrats have argued for the past four years that the nuclear firepower of the four Trident submarines should not exceed that of the Polaris boats they will replace.
Mr Rifkind is expected to announce in a speech to the Centre for Defence Studies in London today that, after a reassessment of nuclear strategy, he sees no need for more warheads.
Though the Government has never said how many warheads are carried on Polaris submarines, each boat is capable of carrying 16 missiles each with three warheads - a maximum of 48. Each US-manufactured D5 Trident missile would be capable of carrying eight warheads - increasing the fleet's firepower to a theoretical 512 warheads. In practice, as with Polaris, only one boat might be deployed at sea.
Tory backbenchers seemed content with the cutback. Sir Geoffrey Johnson Smith, chairman of the Conservative backbench defence committee, said he was 'happy' so long as it meant less pressure on conventional weaponry. 'We don't want to wake up one morning and find the Treasury is taking another big slash at defence.'
Cost savings on missiles and warheads, which would have been manufactured in Britain, will not be great compared to the pounds 10bn capital cost. The first Trident boat, HMS Vanguard, joined the Royal Navy in September, the second is due for sea trials next year and the other two are under construction.
Lord Craig, a former Chief of the Defence Staff, said he would be 'unhappy' about relying on Trident for sub-strategic deterrence. One problem was 'the reliability over a very long period of one missile with one warhead on a single boat which must be at sea'.
Speaking on BBC Radio 4, he envisaged a further problem in relying on the US to service the weapon. Future administrations might not feel the same commitment when the adversary might be quite different from the old Soviet Union, he said.
David Clark, Labour's defence spokesman, welcomed the policy shift. 'Again the Government has been proved wrong. They are making a mess of running our defences and the sooner we have a proper review rather than this fudge and nudge through Treasury-driven cuts, the better,' he said.
Menzies Campbell, the Liberal Democrats' defence spokesman, pointed out that limiting Trident's firepower to that of Polaris had been his party's policy since 1989. 'At last some belated common sense is creeping into the Government's thinking on nuclear weapons. Not only will this save money, but it will give us greater moral authority when arguing the case for nuclear non-proliferation, which is now the most significant threat to security.'Reuse content