When the cabinet was told in December 1971 that the National Union of Mineworkers had called a national strike for January 9, 1972, Edward Heath warned his colleagues that there was a danger of simultaneous strike action in the coal, gas and electricity industries.
The secret contingency plans predicted that there "would be much hardship" if Mr Heath's fear materialised and ministers believed the unions could inflict "serious damage" without putting themselves at risk of reference to the newly established national industrial relations court.
The cabinet was told in the winter of 1971 that the power stations held nine and half weeks of fuel stocks; and industrial and domestic supplies would last for four and half weeks. Disruption of industry would start within a fortnight of a strike being called, and domestic supplies could be kept going for six to eight weeks at "tolerably reduced level".
There was a contingency plan to use troops to move pithead coal stocks by road and rail but the national coal board had warned ministers that it would permanently embitter relations with the unions.
Industrial action in the gas industry would have an even more serious impact with a contingency plan to use 7,300 troops at production plants.
Strikes in the electricity industry would mean power cuts were inevitable and ministers considered restricting families to heating only one room in their homes. Troops would also be needed to operate the electricity stations.
An "early warning system" paper by the central policy review staff - the first Downing Street thinktank which Mr Heath set up under Lord Rothschild - shows that ministers had expected a prolonged miners' strike to be called from September 1971.
In assessing the government's first 15 months in office in the autumn of 1971, the CPRS said that while Mr Heath had successfully negotiated to join the EEC; passed the Industrial Relations Act; cut taxes and introduced "a more serious style of government" there had also been notable failures on inflation, unemployment and Northern Ireland.
