Under what circumstances should criticism of the state of Israel be deemed "illegitimate?" The now-cancelled Southampton University conference, "International Law and the State of Israel: Legitimacy, Responsibility and Exceptionalism", brought this subject into focus. But the question is hardly new.

Those of you with long memories may recall that, in 1956, at the time of the Anglo-French invasion of Egypt, a number of Jewish and - ostensibly - Zionist members of the British parliament found themselves at the receiving end of much communal opprobrium because they criticised Israel, whose armed forces had taken advantage of the invasion in order to neutralise terrorist cells in Gaza and the Sinai peninsula.

The MP for East Willesden - the highly vocal career Labour-Zionist Maurice Orbach - voted with his socialist colleagues to condemn the Anglo-French-Israeli initiative, and was subsequently booted out of his seat in a campaign whipped up by angry Jewish constituents. But in North-West Leicester there were few Jewish voters, and the local Labour MP there, who also voted against the Suez adventure, survived wider, vicious criticism of him. His name was Barnett Janner and, at the time, he was president of both the Zionist Federation and the Board of Deputies. What is more, at the deputies' meeting on November 18, 1956, a large majority expressed full confidence in him.

There was a time when anti-Zionism was not merely a significant force in Anglo-Jewish affairs, it was fashionable. We need to remind ourselves that a former British chief rabbi (Hermann Adler) denounced Zionism from the pulpit, that the founding father of the Federation of Synagogues (Samuel Montagu) was an enthusiastic anti-Zionist, and the founding father of the Liberal Jewish Synagogue (Claude Montefiore) went so far as to blame Zionism for the rise of Hitler.

But into this sombre history lesson we need to inject the word "context." The handful of London- and Manchester-based Satmar chasidim who routinely join anti-Zionist demonstrations are campaigning against a nation-state that exists. The Jewish intellectuals and media personalities who apparently sympathise with them want to dismantle a vibrant liberal democracy -Israel - to have it replaced with a larger political entity in which antisemitism will be permitted to flourish. On paper, the "one state" that these extremes of left and right desire would be a purely secular entity. In practice it would become an Islamists' paradise.

They deny to Jews that which they allow other ethnicities

In principle, today, we ought still to be able to distinguish anti-Zionism from antisemitism. In practice, the one has merged with the other. Anti-Zionists do not oppose the creation of a Jewish nation-state - such a state already exists. What they oppose is the continued existence of a Jewish nation-state. In seeking to dismantle that state, therefore, they expose their antagonism towards the very concept of Jewish self-determination.

This is true especially of those who deny that there is any such entity as a Jewish "nation". These positions are inherently racist: they deny to the Jews that which they freely grant to other ethnicities, and they do so on purely ethnic or racial grounds.

None of this means that policies of Israeli governments cannot be legitimately criticised. Of course they can. But we need to recognise that, fundamentally, what drives the BDS movement is not antagonism towards Jewish settlements in Judea and Samaria, but hostility towards the concept of Jewish nationhood. This truth has been recognised by no less an opponent of the settlements than Professor Norman Finkelstein who, in 2012, launched a blistering attack on the Palestine Solidarity Movement's campaign for the "right of return", condemning it as a cover for its ambition to destroy Israel.

Finkelstein was absolutely right. Criticise Israel, if you must, to your heart's content. Demonstrate to your utmost against Israeli domestic or foreign policy.

But do not espouse a cause that calls, even if indirectly, for Israel's destruction and expect not to be condemned as a racist. For that is what you are.