The BBC's Newsnight program, broadcast late Wednesday, said government papers held at the National Archive show Britain shipped 20 tons of heavy water to Israel in 1959. The program said the water was vital for the production of plutonium at Israel's secret Dimona nuclear reactor in the Negev desert.
Newsnight said British officials did not impose any conditions on the sale, such as stipulating the heavy water could be used only for peaceful purposes. The BBC report said the United States had refused to supply heavy water to Israel without such safeguards.
Robert McNamara, who became President Kennedy's defense secretary in 1961, told the BBC that Britain didn't inform the Americans it had sold heavy water to Israel.
"The fact that Israel was trying to develop a nuclear bomb should not have come as any surprise ... . But that Britain should have supplied it with heavy water was indeed a surprise to me," he said.
In one of the documents, a British Foreign Office official cautioned against informing the United States of the sale.
"On the whole I would prefer NOT to mention this to the Americans," Foreign Office official Donald Cape wrote in an official paper at the time, the BBC said.
Israeli Vice Premier Shimon Peres, who was director general of Israel's defense ministry from 1953 -58 and was instrumental in building Israel's nuclear reactor in Dimona, refused to comment on the report Thursday.
There was no immediate comment from Britain's Foreign Office.
The Israeli nuclear reactor at Dimona in the Negev desert is one of the most sensitive sites in Israel. Israel maintains a policy of deliberate ambiguity about its nuclear program, neither confirming nor denying that it has nuclear weapons.
It has said that the Dimona reactor is used only for peaceful purposes.
In 1986 former technician Mordechai Vanunu gave information and pictures of the Dimona facility to London's Sunday Times. On the basis of his revelations, experts concluded that Israel has the world's sixth-largest stockpile of nuclear weapons, consisting of hundreds of warheads.
Vanunu was freed in April after spending 18 years in prison for espionage and treason for divulging that information.
Because it has resisted international pressure to sign the Nuclear Nonproliferation Treaty, Israel does not formally have to declare itself as a weapons state or agree to any curbs on its nuclear activities.
In 1995, Peres declared, "Give me peace, and we will give up the atom. If we achieve regional peace, I think we can make the Middle East free of any nuclear threat."
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 by civil servants, mainly in the Foreign Office and the UK Atomic Energy Authority.
The documents reveal the heavy water was transported from a British port in Israeli ships in two consignments, half in June 1959 and half a year later.