THE UK DEPLOYED TRIDENT NUCLEAR missiles because they could cause the total breakdown of Russian cities by killing half their inhabitants, according to a top-secret document passed to the Sunday Herald.
To ensure that the warheads inflicted "unacceptable damage" on Moscow and St Petersburg, the government was prepared to explode them at ground level to maximise lethal levels of radioactive contamination.
These revelations are considered so sensitive that the Ministry of Defence (MoD) has tried to cover them up in case they hamper current plans to replace Trident. Senior officials are still carrying out the same kind of "Dr Strangelove arithmetic", critics say.
The decision to adopt the Trident system was taken in 1980 by the then prime minister, Margaret Thatcher.
As a result, up to 200 warheads are now stored at Coulport on the Clyde and deployed on submarines.
But the assumptions behind the decision have been a secret until now. They are revealed in a document prepared in 1978 for the then chief scientific adviser to the MoD, Professor Sir Ronald Mason.
This document, among others, was removed from the National Archives in London last year at the insistence of the MoD, which says they had been released in error. But it had already been photographed by nuclear researcher Brian Burnell.
Stamped "top secret" on every page, it describes the level of "generalised destruction" the UK would be prepared to wreak on Russian cities in order to deter a nuclear attack on the UK.
The key criterion, it says, "is based not on destroying the whole city or killing a specified number of people, but instead on creating sufficient damage to bring about the breakdown of the city as a functioning community."
This could be accomplished, the document argues, by inflicting "severe structural damage" across 40% of a city. If the bombs were exploded in the air above the city, this would be likely to kill at least 40% of the inhabitants instantly and seriously injure a further 15%.
But the document then points out that up to 30% of city populations could be sent to underground bunkers. These would protect people against bombs exploded in the air, it says, but not those detonated at ground level.
"Ground-bursts would subject 55-60% of the city to a radiation dose sufficient to cause rapid debilitation followed by death for most people in the area, and to contaminate food, water, air and both damaged and undamaged buildings," the document states. "Residual radiation would remain a hazard for many years to come."
According to a Foreign Office report last week, the UK's nuclear policy is to "deliberately maintain ambiguity about precisely when, how and at what scale we would contemplate use of our nuclear deterrent."
John Ainslie, co-ordinator of the Scottish Campaign for Nuclear Disarmament, accused the government of deliberately hiding the document to avoid a proper debate on replacing Trident. "They don't want anyone to think seriously about the possible targets of British nuclear weapons or the consequences of using them," he said.
"So long as this country deploys nuclear submarines, there will be officials somewhere carrying out the Dr Strangelove arithmetic required to target these horrific weapons of mass destruction."