By Paul Dwyer
Producer, Windscale: Britain's biggest nuclear disaster
Fifty years ago, on the night of 10 October 1957, Britain was on the brink of an unprecedented nuclear tragedy.
The Windscale piles provided material for nuclear weapons
A fire ripped through the radioactive materials in the core of Windscale, Britain's first nuclear reactor.
Tom Tuohy, the deputy general manager at the site, led the team faced with dealing with a nightmare no-one had thought possible.
"Mankind had never faced a situation like this; there's no-one to give you any advice," he said.
Tuohy and his men were confronted by a terrifying dilemma.
If they let the fire burn out, it could spread radioactivity over a large area of Britain. But if they put water on the reactor, they risked turning it into a nuclear bomb that could kill them all.
"I phoned the general manager," Tuohy recalled, "and said, 'look, I want to turn on the water'.
"I thought if it goes up, we will all go with it," remembers Margaret Davis, whose husband Eddie was also engaged in the emergency operation. "I've never been so frightened in my whole life."
Now tapes of the inquiry into the accident, heard for the first time in a BBC film, reveal the reasons why the politicians covered up the causes of the accident.
Scientists had been warning about the dangers of an accident for some time.
The safety margins of the radioactive materials inside the reactor were being further and further eroded.
"They were running much too close to the precipice," says Dr Dunworth, a senior manager in the Nuclear Research Laboratory in Harwell, Oxfordshire, who was one of those highlighting the potential dangers.
But the politicians and the military ignored the warnings; instead they increased demands on Windscale to produce material for an H-bomb.
Graphite overheated and fire broke out
Air from fan fuelled fire
Nuclear contaminants travelled up chimney
Filter blocked some but not all contaminated material
Radioactive cloud spread over UK and Europe
A succession of prime ministers since the war had been determined to persuade the Americans to share the secret of their nuclear weapons with Britain.
Prime Minister Harold Macmillan believed that, if Britain could develop an H-bomb on the scale of the Americans', they would treat it as a nuclear equal and form an alliance.
Even as Tuohy and the Windscale men faced their nuclear nightmare, Macmillan was arranging a summit in Washington where they would announce the Declaration of Common Purpose.
"It's a unique agreement between two nation states," says Professor John Baylis of Swansea University. "A superpower sharing its nuclear secrets with another."
It laid the foundation of Britain's current "special relationship" with the US - but the Windscale disaster threatened to end it before it began.
At Windscale, Tuohy's gamble paid off.
By turning on the water and shutting off the air, they managed to put out the fire and avert a tragedy.
It was a moment of profound relief, he says. "You've got this blazing inferno with these flames belting out; to know that you've licked it, that was a marvellous feeling."
Macmillan realised that if the American Congress knew that the fire had been the result of reckless decisions taken to try to produce the-H bomb, they might veto Macmillan and Eisenhower's plans.
An inquiry revealed how the accident was covered up
Faced with such a possibility, "he covered it up, plain and simple", says his grandson and biographer, Lord Stockton.
Macmillan issued a report that said the accident had been caused by "an error of judgement" by the Windscale workers.
For 50 years, the official record on the accident has been that the very men who had averted a potentially devastating accident were to blame for causing it.
"I resented it at the time," says Peter Jenkinson, who was an assistant physicist at the reactor, "and I hoped the record would be put straight."
After the inquiry, he and his colleagues finally got their wish.
Windscale: Britain's biggest nuclear disaster was broadcast on Monday, 8 October, 2007, at 2100 BST on BBC Two.
BBC Radio 4 broadcast a two-part drama about Windscale on Monday and Tuesday, 8 and 9 October, at 14:15 BST.