According to interesting new research by Michael Crick and BBC Newsnight Harold Wilson's government in the 1960's allowed the sale of highly sensitive materials, including heavy water and plutonium, to Israel for use in its atomic bomb programme.
So secret was this that Government ministers were deceived and lied to about what was going on, and the Americans, despite the various UKUSA agreements pertaining to nuclear materials, were deliberately kept in the dark.
It is conceivable that Wilson himself did not know what his officials were actually doing. Senior civil servant at the ministry of science Michael Israel Michaels (his real name) arranged for a sample of plutonium to be sold to the Israelis, despite the strong protestation of the Defence Intelligence Service. This gave the Israelis a head start when it came to handling their own plutonium from the reactor at Dimona. Moreover that reactor only functioned through the use of heavy water (deuterium oxide) as a moderator, nominally sold to them by the Norwegians, but FROM Britain....(the British and Israeli negotiators were in seperate rooms, with Norwegians shuffling between the two
Other key components of nuclear weapons were also sold to Israel including uranium 235, highly enriched lithium 6 and two tonnes of unenriched lithium. (Plus instruments such as dosimeters).
By the time the Israelis lauched their aggressive war of 1967, they had two crude nuclear bombs as their trump card.
Michael Michaels retired in 1971 but was then employed in London by the Government of Israel. He died in 1992.
Jack Straw (UK foreign secretary) has conceded that the British government of the day knew the heavy water at least was bound for Israel. He has yet to acknowledge this to the IAEA, where he is currently explaining the dangers of nuclear proliferation concerning Iran.
(And what about the French? Sure, we gave them some plutonium years before, but that was secret too so no-one knows ok)