A seasoned observer of the British trade union scene put it to me in stark terms. “You’d be hard put,” he said, “to find a union in the UK that isn’t sympathetic to the boycott of Israel.”

His observation was made in a conversation which took place a few days before the Transport and General Workers Union (TGWU) voted, at its conference, to back the boycott of Israel. That vote, on July 4th, brings the number of British unions supporting the boycott campaign to four: journalists, academics, public and voluntary service workers and now the union representing those working in an array of industries from transportation to food.

The TGWU’s debate reproduced the same themes which emerged at the other union conferences. Firstly, the portrayal of Israel as country forged in colonial sin and therefore solely responsible for all the conflicts in the area, including the recent bout of intra-Palestinian bloodletting in the Gaza Strip. Secondly, the indignant protest that a boycott of Israel can never be, by any stretch of the imagination, antisemitic.

When the University and College Union (UCU) passed its boycott resolution back in May, it stated explicitly that “criticism of Israel cannot be construed as anti-semitic.” Addressing the delegates to the TGWU conference, Barry Camfield, the union’s deputy general-secretary, thundered, “We will not have the Israeli state telling us that the boycott is antisemitic.”

Other delegates said much the same. For Brid Smith, one of those proposing the boycott motion, it was all quite simple: “We are refusing to buy Israeli products, not Jewish products.”

That distinction only works for those who believe that antisemitism is, in any case, a rhetorical device designed to muzzle criticism of Israel. For the rest of us, the antisemitism embedded in these union resolutions is painfully clear. Israel alone is selected for boycotts and demonization, Israel alone is a moral deformity among the nations of the world.

In recent weeks, there has been much agonizing over why British unions are particularly prone to boycotts and so contemptuous towards claims of antisemitism. A variety of credible explanations have been offered, among them: that Britain feels guilty about the Balfour Declaration of 1917, that the far left is unusually strong in the union movement, that bashing Israel is a way of bashing Tony Blair, the recently departed Prime Minister who is loathed by the extremists for his steadfast alliance with the United States.

But there is another question, which is particularly pertinent given the sad possibility that other British unions, including the umbrella body, the Trades Union Congress (TUC), might also sign up to a boycott: does it mean anything, in practical terms?

In some ways, this is a question about the political clout of Britain’s unions. From the nineteenth century onwards, trade unions played an increasingly central role in the country’s political life, but by the last two decades of the twentieth century, following bruising conflicts with Margaret Thatcher’s Conservative government, the unions were demoralized and politically broken.

The advent of a Labour Party government in 1997 did not restore the trade union movement’s political fortunes. Tony Blair was a moderniser who pushed his party towards the center; his successor, Gordon Brown, is likely to keep it there.

Marginalized, distrustful of Blair’s agenda and infuriated by his support for the war in Iraq, British unions have become more and more prone to radical posturing. That they are a thorn in the side of the government is indubitable.

Currently, there are six and a half million trade unionists in Britain, roughly ten per cent of the population. The vast majority of them do little more than pay their union dues. It’s a safe bet that most of the 2.2 million members of the four unions which endorsed a boycott of Israel had no idea that this course of action was being considered until it was too late. And when ordinary members protest, as has happened with particular force inside the National Union of Journalists, union leaders respond by waving the rule book. Their purpose in doing so is to mire any anti-boycott ardor in the fog of bureaucracy.

Yet what matters, ultimately, is not how representative these unions are of their members, but the policies they promote. And the policy they are promoting towards Israel is based upon a theme familiar to students of Jewish history: exclusion.

The boycotters know they will not change government policy overnight. Rather, they have embarked on a stealth strategy whose goal is to turn the exclusion of Israel into a social norm, so commonplace that it becomes unremarkable. Then, they believe, governments will listen. That is why the boycott matters - and why we must fight it at every turn.

Ben Cohen is Associate Director on antisemitism and extremism at the American Jewish Committee.