Government documents released at the Public Records Office yesterday also reveal that while Macmillan told the House of Commons in May 1958 that Britain possessed thermonuclear weapons, a usable hydrogen bomb was not produced until late 1960.
The records show that, up to the beginning of 1961, the British nuclear deterrent consisted of, at most, 40 powerful atomic bombs with yields of between 0.5 and 1 megaton. The UK first tested H- bombs in May 1957 but more tests in November 1957 and in April and September 1958 were needed to develop the design. Assembly of 'Red Snow', the first thermonuclear weapon, did not start until late 1959. In April 1959, Macmillan was told that if assembly of Red Snow was to start by November that year, a building costing nearly pounds 700,000 would have to be constructed at Burghfield, but that it would take at least three months to check assertions by the UK Atomic Energy Authority (then responsible for Britain's nuclear weapons programme) that making Red Snow at Burghfield was 'an acceptable risk'.
Within a month, Macmillan authorised the construction 'before we had completed an exhaustive examination of the safety procedures needed for the manufacturing operations', as one minute from the Minister of Aviation records. It was not until July 1960, more than a year later, that Macmillan was told that the authority's assurances were correct.