Britain secretly sold Israel an important ingredient for the nuclear program in the 1950s, according to the documents uncovered.
The BBC's Newsnight program said government papers held at the National Archive showed Britain shipped 20 tones of heavy water to Israel in 1959.
The program said the water was vital for the production of plutonium at Israel's top secret Dimona nuclear reactor in the Negev desert. Newsnight said British officials did not impose any conditions on the sale, such as its being used for peaceful purposes, and in one of the documents a British Foreign Office official cautioned against informing the United States of the sale.
The revelation is potentially embarrassing for the British government at a time when London is heavily engaged with its European Union partners in trying to persuade Iran to give up its nuclear ambitions.
"On the whole I would prefer NOT to mention this to the Americans," Foreign Office official Donald Cape wrote in an official paper in 1958.
Israeli Vice Premier Shimon Peres, who was director general of Israel's Defense Ministry from 1953-1958 and was instrumental in building Israel's nuclear reactor in Dimona, on Thursday refused to comment on the report.
There was no immediate comment from Britain's Foreign Office.
Israel has said the Dimona reactor is used only for peaceful purposes and nuclear experts said Thursday that heavy water can also be used for civilian purposes.
Heavy water, also known as deuterium, is used both as a reactor coolant and as a moderator in the process of turning natural uranium into weapons-grade plutonium.
The Dimona reactor is one of the most sensitive sites in Israel. The state maintains a policy of deliberate ambiguity about its nuclear program, neither confirming nor denying that it has nuclear weapons.
According to Newsnight, the 20 tones of heavy water were part of a consignment that Britain bought from Norway in 1956. Britain later decided this was surplus to requirements.
According to the BBC, the documents show how officials presented the transaction as a straight sale from Norway to Israel. The documents reveal, however, that the heavy water was transported from a British port in Israeli ships in two consignments, half in June 1959 and half a year later.
Newsnight said it had found no evidence that ministers in the government of then Prime Minister Harold Macmillan were aware of the sale and believed the decision was taken simply by civil servants, mainly in the Foreign Office and the U.K. Atomic Energy Authority.
Norwegian Foreign Ministry spokeswoman Anne Lene Dale Sandsten disputed the claim that Britain was involved.
"It was Norway that exported heavy water to Israel. This has been known for a long time," she said Thursday, declining to comment further on the report.
Israel's Atomic Energy Commission said it was investigating the report, but had no comment at the moment.
According to Gerald Steinberg, an expert on the Israeli nuclear program from the Bar Ilan university's Begin-Sadat center for strategic studies, the British shipment may have been part of an exchange following the 1956 Suez campaign.
"Israeli nuclear facilities were being developed in cooperation with France and there was a Suez connection there, so there may also be a possible less visible connection with Britain," Steinberg said. "This was before the era of the Non Proliferation Treaty, so there were no international restrictions at the time."
In 1956 Israel invaded the Sinai to give Britain and France a pretext to send troops into Egypt and retake the strategic Suez canal which had been nationalized by late Egyptian leader Gamal Abdel-Nasser. The British and French quickly withdrew following intense pressure from the U.S., which had not been informed of the attack.
Steinberg said heavy water can also be used for peaceful purposes. He noted that it is already known that Israel bought heavy water from Norway.
"This revelation does not tell us anything new about the Israeli program," he said.
In 1986, former technician Mordechai Vanunu gave information and pictures of the Dimona facility to London's Sunday Times newspaper. On the basis of his revelations, experts concluded that Israel has the world's sixth-largest stockpile of nuclear weapons, consisting of about 200 warheads, the AP reports.
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