Britain is being accused of trying to cover up its role in helping Israel develop its nuclear weapons programme.
In August, Newsnight revealed that more than 40 years ago, Britain sold heavy water, a key substance, to Israel.
MPs now allege that minister Kim Howells tried to mislead the International Atomic Energy Agency (IAEA) over Britain's role.
The charges come as the head of the IAEA, Mohamed ElBaradei, is about to the receive the Nobel Peace Prize.
Mr ElBaradei will receive the Prize this weekend for his and the IAEA's work in curbing the spread of nuclear weapons.
The shipments involved heavy water - a key element in producing plutonium - which the UK had originally bought from Norway.
Officially it was sold back to a Norwegian state firm called Noratom. But Britain knew Noratom would immediately sell 20 tons of the heavy water to Israel, and it was even collected directly from a British port by Israeli ships.
It's thought that today Israel possesses more than hundred nuclear weapons.
After Newsnight's original broadcast, the Arab League wrote to the IAEA seeking a full investigation.
But Foreign Office minister Kim Howells told Mohamed ElBaradei that Britain did not sell the material to Israel.
"The UK was not in fact a party to the sale of heavy water to Israel," he wrote, "but did negotiate the sale back to Norway of surplus heavy water."
Britain then circulated that response to every IAEA member government; but opposition MPs are accusing the Foreign Office of using Norway's involvement as a smokescreen.
Liberal Democrat Foreign Affairs spokesman Sir Menzies Campbell told Newsnight: "There's an old political dictum that it's not the event that is often the most embarrassing, it's the cover-up.
"The trouble with this cover-up is that this is not a cover-up. It simply flies in the face of the known facts, now that we have access to previously classified documents.
Labour MP Jeremy Corbyn is asking the Foreign Affairs Select Committee to investigate Kim Howells' response to the IAEA.
"It's simply untrue - right back to the late 1950s we were a party to the transfer of nuclear technology to Israel," he said.
"We were party to the development of a nuclear facility in Israel that could, and has, been used for the manufacture of nuclear weapons; Norway was always a smokescreen."
Surprise in Washington
Newsnight's initial report last August was based on documents unearthed in the British National Archive, and shocked people around the world.
In Washington President Kennedy's former Defence Secretary Robert MacNamara, who tried to stop Israel going nuclear, told Newsnight: "The fact Israel was trying to develop a nuclear bomb should not have come as a surprise, but that Britain should have supplied it with heavy water was indeed a surprise to me."
Newsnight has tracked down Donald Cape, one of the Foreign Office officials involved in deciding that British heavy water should be shipped to Israel.
In September 1958 Cape received a letter in which the UK Atomic Energy Authority (UKAEA) admitted: "It could be argued that the Israelis will receive the heavy water by reason of our reselling it to Noratom; that therefore we are parties to the supply to Israel."
Mohamed ElBaradei will receive the Nobel Peace Prize
Mr Cape agrees with Kim Howells' interpretation, however, and insists the heavy water was sold to Norway.
It is "absolute nonsense", he says, to suggest Norway's involvement was a "sham" and that the real sale was from Britain to Israel.
But Newsnight has also obtained Israel's contract with the Norwegian firm Noratom. It says Noratom would provide heavy water from the UKAEA for Israel - delivered in Britain to Israel.
Noratom would take a commission of two per cent on the four million dollar deal; its responsibility would be "limited" to that of "consultant".
Donald Cape says he and his colleagues did not tell ministers about the transaction because there was no reason for either Britain or America to suspect what Israel was up to.
But confidential letters obtained by Newsnight through a Freedom of Information request, written two months before the first delivery was collected by Israel, suggest there were already suspicions about Israel's intentions.
The documents show the Foreign Office knew Israel had secretly tried to buy uranium from South Africa - without safeguards.
One letter quotes secret CIA reports from 1957 and 1958, which took the view: "The Israelis must be expected to try and establish a nuclear weapons programme as soon as the means were available to them."
The man who wrote these Foreign Office letters was Donald Cape himself.
When the existence of the Israel's nuclear reactor at Dimona was revealed to the world in December 1960, Britain's spymasters made an assessment of Israeli capabilities.
In the last few days, Newsnight has obtained the top secret 'UK eyes only' report - previously only seen by the bosses of intelligence bodies such as MI6, MI5 and GCHQ.
These minutes are really the only occasion on which the British Government has ever released a detailed assessment of Israel's nuclear weapons programme, and they show just how important Britain's 20 tons of heavy water were to that programme.
According to the Joint Intelligence Assessment, it meant that the Dimona reactor would be able to make enough plutonium to build up to six atom bombs a year.
The document concludes: "It has been, and remains our opinion, that Israel wanted an independent supply of plutonium so as to be in a position to make nuclear weapons if she wished."
Yet we also know that the Foreign Office imposed no restrictions on what the heavy water would be used for.
Donald Cape wrote that it would be "over zealous" to impose safeguards on Norway or Israel. And he agreed to keep the deal secret even from the US, writing that: "I would prefer not to tell the Americans."
Says Menzies Campbell: "There's no doubt we deceived our close allies, the United States; we knew that there was likely to be a military use to which this heavy water was put.
"The material went from [the UKAEA at] Harwell direct to a British port, to Israeli ships, and was then taken to Israel.
"This assertion that somehow we weren't party to the action simply does not stand up when you analyse the facts."