The Irish are 'in' for the moment, and the Jews 'out', as recipients of the sympathy of the international left," wrote Conor Cruise O'Brien caustically in his book The Siege: The Saga of Israel and Zionism (1986).

Faber reissued the book last year, with a foreword by me, and its assessment of Israel's dilemmas stands up well 30 years on. The politician that O'Brien is referring to is Ken Livingstone. That was prescient, as Livingstone's tendency to make eccentric historical assertions about the Jews and many other subjects remains undimmed. The difference is that his ideological co-thinkers are now in control of the Labour Party. Hence for Labour's leaders, despite the party's close historical links with Israel, the Jews are currently "out". It wasn't always this way, even on the far left.

When Jeremy Corbyn faced questions in his leadership campaign last year about past alliances with a Holocaust denier, his supporters were indignant - and for entirely the wrong reason. A pressure group called Jews for Justice for Palestinians complained of "the use - and serious abuse - of accusations of antisemitism and the like". It's a theme of today's far left that accusations of antisemitism are made too lightly, and it's a myth. Commentators in forums like the JC are careful to avoid alarmism in their assessment of the threats to British Jewry. Though I'm dismayed by Mr Corbyn's rise and will not vote Labour again while he remains leader, I've never accused him of antisemitism.

Yet there was a time in post-war history when the far left itself made vitriolic and unfounded accusations of antisemitism. I was reminded of this by reading my colleague David Aaronovitch's absorbing new book Party Animals, recounting his upbringing in a Communist family. Among many acute reflections on the misguided idealism of his parents and their comrades, Aaronovitch notes that the Western security services did, after all, have grounds to question the loyalty of Communists. One case that leads him to this reconsideration was "an infamous part of Cold War history", the execution in the US of Julius and Ethel Rosenberg in 1953.

The Rosenbergs had been convicted of espionage. Their case was a cause célèbre of the left and Soviet diplomacy, which claimed the couple, who were Jewish, had been framed in a frenzy of American antisemitism.

So long as values of pluralism are defended Jews are safe

Sending the Rosenbergs to the electric chair was morally abhorrent yet we now know that the charges were correct and they were guilty. Julius Rosenberg was the head of an espionage ring passing atomic secrets to the Soviet Union. The campaign protesting the Rosenbergs' innocence was fraudulent. It was manufactured in part to divert world attention from the antisemitic purges then taking place in the Soviet bloc, such as the show trial and execution in Czechoslovakia of the Communist official Rudolf Slansky.

Those seem distant times. Communism in eastern Europe failed. Though antisemitism in Western societies remains stubborn, it has dwindled. Despite the recent terrorist atrocities in Brussels, Paris and Copenhagen, I'm hopeful for the security and flourishing of Europe's Jews. My reasoning is the resilience of European democracies. So long as constitutional societies are prepared to defend the values of pluralism and refuse accommodation with apologists for terrorism, Jews have safety.

There's no room for complacency, of course. Yet I firmly believe the left destroys itself as an electoral force by abandoning that struggle, and will have to come back to it if it's to regain public trust.