The fleet of four US-designed Trident submarines will go ahead, but the number of warheads on the 16 missiles each boat will carry will be slashed from a maximum of 512 to about 192, the total carried by Polaris, which it is to replace.
Defence ministers are also close to agreement that some Trident weapons will carry a single nuclear warhead, enabling it to take on the sub-strategic role assigned to aircraft armed with free-fall nuclear bombs. That would allow big savings by cancelling plans for a bomber-launched tactical air-to-surface missile (TASM), and making possible further cuts in Tornado squadrons.
A decision to abandon TASM is likely to be announced in July in the defence White Paper, according to ministerial sources, but the details about the scaling down of the Trident warheads may never be made public.
Each missile would have carried up to eight independently-targetable warheads, compared with three on each Polaris. Ministers, under pressure to cut spending, decided the diminishing threat from the former Soviet Union meant Trident no longer needed to penetrate 'hardened' targets in Moscow.
The use of Trident to carry a sub-strategic weapon is seen as an insurance against a nuclear attack from potential Middle East enemies using unsophisticated missiles such as Scuds, fired by the Iraqis against Israel during the Gulf war.
Limiting the number of Trident warheads to about that of the Polaris force will be seen as a victory by the Liberal Democrats and Labour, who fought the last election on a campaign of minimum deterrence.
The expected change of policy was welcomed by Menzies Campbell, the Liberal Democrat spokesman on defence. But he was 'sceptical' about the wisdom of maintaining a sub-strategic system on Trident.
The MoD is facing up to pounds 2bn in cuts over the next three years. Options being studied include scrapping a squadron of 12 Tornado fighters, reducing RAF and Navy strength by 5,000 each, reducing the number of frigates and destroyers from 40 to 35, reducing tank orders from 400 to 320, and cutting the Territorial Army by 5,000.Reuse content