It's hard to imagine anything quite so damaging for the Netanyahu government right now as the release of official documents showing that Israel offered to sell nuclear weapons to South Africa during the apartheid era.

It's not just the confirmation that Israel does indeed possess such weapons (in at least three different sizes, apparently) but that it was prepared to engage in nuclear proliferation by supplying them to what at the time was a pariah state.

There are basically three dimensions to this:

One. Israel will no longer be able to maintain its policy of "nuclear ambiguity". As the only nuclear-armed state in the Middle East, it will have to be included in future discussions about non-proliferation and disarmament in the region – whether it wants that or not.

Israel, which along with North Korea, India and Pakistan has long resisted joining the non-proliferation treaty, will now come under increasing pressure to sign it and allow inspectors in.

Two. This blows a large hole in Israel's argument that Iran must not be allowed to develop nuclear weapons. Part of its case is that the Iranian regime, if it does get the Bomb, cannot be trusted not to supply it to others. It's now clear that Israel cannot be trusted on that score either.

Three. The fact that Israel's intended nuclear customer was South Africa, and its warm relations at the time with racists like John Vorster (a former supporter of Hitler), will invite the drawing of further parallels between apartheid in South Africa and what is happening in Israel today.

Israel reportedly tried to stop the incriminating documents being released, so presumably it has had time to prepare some kind of explanation – though on past form it may refuse to say anything and hope that the issue will go away. But while the Iranian nuclear programme remains in the spotlight it's going to be very difficult to ignore.