The old 1930s US mine workers' chant, Which Side Are You On? still has a resonance for the trade union movement across the world.

This week the TUC decided which side it was on. It chose a tiny ultra-left UK fringe organisation, the Palestine Solidarity Campaign, over its comrades in the Israeli trade union the Histadrut, and the Palestinian General Federation of Trade Unions (PGFTU). With their ill-judged motion and amendment, Unite and the Public and Commercial Services Union thus ends 60 years of mutual struggle.

How has this happened? Part of the answer is that Andrew Murray, chair of the Stop the War coalition, now has an unchallenged position as "chief-of-staff" at Unite, Britain's most powerful union. The Unite motion, which calls for withdrawal of UK forces from Afghanistan, the immediate cessation of Nato action in Libya and recognition of the state of Palestine, might as well have been taken from Mr Murray's Twitter feed.

But the TUC leadership must also shoulder responsibility for allowing this betrayal of the principles of international solidarity. Until now, General Secretary Brendan Barber has held the line against a growing anti-Israel sentiment in British trade unionism. He could at least have explained the importance of the work carried out by the Histadrut and the PGFTU, in conditions unimaginable to most British trade unionists.

The infantile politics of the unions stand in stark contrast to the mature approach being taken by the UJS for students starting courses this year. Far better, surely, to promote peace and the two-state solution than encourage a damaging breach with comrades in Israel that could take years to mend.