Threats that civilisation would be devastated by “nuclear winter” after conflict with the Soviet Union were dismissed as scaremongering, according to Home Office files.

Officials were more interested in monitoring the activities of campaigners opposed to cruise missiles, documents released by the National Archives in Kew reveal.

A confidential file on “Nuclear winter – global atmospheric consequences of nuclear war” shows that civil servants in the department’s emergency planning section, F6, decided they did not need to research the disputed phenomenon.

An internal memo in December 1984 records: “It was agreed with F6 that no assessment of the [nuclear winter] theory would be carried out by the branch and as such our interest is limited to general reading which could not be regarded as following the subject in any depth.”

The theory predicted that multiple exchanges of nuclear warheads would result in firestorms generating massive black smoke clouds that would rise into the stratosphere, blocking out sunlight and depressing temperatures at ground level around the Earth for months if not years. It had gained popular currency with the release of the US television film The Day After in 1983 and the BBC’s Threads in 1984, both of which dramatised the consequences of a nuclear conflict.

After newspaper reports that American scientists had confirmed the hypothesis, MPs who sought advice were provided with a briefing note informing them: “The government believes that the outbreak of war is extremely unlikely and our policy of deterrence is aimed at keeping it that way.”

Another Home Office memo records: “This theme has been taken up with enthusiasm by the anti-nuclear movement, which has tended to present the nuclear winter … as accepted scientific fact ignoring important qualifications expressed even by scientists working on the theory. Unfortunately such a presentation has been generally accepted by the public.”

Closer attention was paid to anti-nuclear activists. “CND is planning to … recapture its earlier momentum by major campaigns against cruise and Trident in 1985,” the Home Office files note. ”The main focus of its protest activity will switch to RAF Molesworth and will involve increased willingness to use tactics of civil disobedience to disrupt construction work at the site.”

Faslane Peace camp, according to one memo, “is reported to be bankrupt”. CND itself, the Home Office, concluded, “is no mere front organisation and there is no evidence of Soviet funding”.

The Greenham Common women, it was said, received support from CND and other organisations, “although some are clearly uncomfortable about their strident all-female attitude”.

Anti-nuclear groups were under surveillance. “Data is now collected on demonstrations and incidents by anti-nuclear groups at MoD establishments,” the file states.

In the battle for public sympathy, pro-nuclear groups received official help. “Continued government support – both financial and through the provision of nuclear PR material – will be necessary,” one report records. “Co-ordination of [their] activities … is best left, in general, to the groups themselves although periodic advice and encouragement from ministers will continue to be valuable.”

Architectural drawings of DIY nuclear blast-proof shelters were commissioned for the latest edition of the Protect and Survive pamphlets. They suggested householders excavate holes in their living rooms and build “igloo shelters”; the components cost £554 – about £1,500 in today’s money.

Facebook Twitter Pinterest Drawings of a nuclear shelter from the pamphlet

Preparations for BBC emergency broadcasting in the event of a war came up against the realisation that it would be difficult to protect transmitters against the destructive effects of electromagnetic pulses caused by nuclear explosions.

“The primary purpose of broadcasting to the outside world after a nuclear attack,” one letter remarked, “would presumably be to let the world know that organised society still existed in the UK.”

The corporation’s World Service submitted a plan to provide a 24-hour, worldwide service from six sites that would have to be nuclear “hardened”. It included rations for “10,000 man days” and protective clothing. The estimated cost was £15.8m (about £44m now).

“Our immediate reaction is that these proposals are based on a much too ambitious specification which we simply cannot afford,” a Foreign Office official responded.

A separate memorandum was headed: “Spontaneous evacuation of civil population in a future war.” A weary civil servant observed: “Another hare, the breakdown of public morale in a war emergency and consequent flight from the capital, was let loose.

“This is a hoary subject in the civil defence planning world (as opposed to the real world) on a footing with others such as ‘will staff turn up for duty on the day?’

“No one doubts the need to maintain a war effort … If the public is not with the war effort then the war would be loseable without a single nuclear weapon being exploded on England’s green and pleasant land.

“The guts of the matter is that in a war emergency a task of the police would be to ensure that, as it does in peacetime (eg peak holiday weekends), that the country does not come to a grinding halt through traffic congestion howsoever caused.”