And then there were three. Usdaw, the shopworkers' union, has followed Unison and the GMB in demanding Labour adopt the full International Holocaust Remembrance definition of anti-Semitism.

Paddy Lillis, its general secretary, tells the Jewish News that the party must adopt the definition and all of its examples "immediately". He is the third union chief to have done so in three days, after Tim Roache on Thursday and Dave Prentis, who set out his reasoning in the New Statesman yesterday.

Why does it matter? These interventions are not empty gestures but are in fact shifting the dial towards defeat for the party leadership. Of the 13 trade union seats on Labour's 39-strong ruling national executive committee, Usdaw, Unison and the GMB each hold two. That all three have come out for the full IHRA definition increases the likelihood that the NEC could overrule the leadership when it votes on the issue on 4 September..

That isn't to say the entire union vote on the NEC will swing behind full IHRA. In an intervention that was in every sense the exact opposite to Lillis's, Ian Hodson, the Bakers' Union president, told Skwawkbox earlier today that his union's NEC representative would support the existing code of conduct. Smaller, left-dominated unions such as his, ASLEF, the CWU and the FBU, however, have only one seat each. Unite, Corbyn's biggest union supporter, is entitled to two but the elevation of Jennie Formby to general secretary means it will only have one until after Labour conference, and, indeed, the vote on IHRA.

Usdaw's intervention nudges the arithmetic in favour of those who wish to see IHRA implemented in full. While they do not yet have a majority on the NEC – by my count, and on current evidence, they are probably two or three votes short – there is much less convincing left to do. Strikingly, Lillis, Roache and Prentis each employed the same argument: that Labour must assuage the fears of the Jewish community, unite, and take the winnable fight to the Conservatives on economic issues (Hodson's argument boils down to fealty to Corbyn).

That is also the argument favoured by Momentum's Jon Lansman, who has not denied reports he is lobbying for Labour to adopt the full IHRA text. The NEC adopted the code of conduct without a vote last month, but pledged to consult the Jewish community further. The answer has been resounding and unambiguous: adopt IHRA in full. Were Lansman and other union representatives or one or the three frontbenchers on the NEC vote for it defeat for the leadership would be close to certain.

Whether the current code of conduct will survive is likely to be determined by the union leaders who have yet to pronounce on the IHRA. Jewish newspapers are beating paths to their doors. Watch this space.