Higher education unions might have known better than to get themselves entangled in the web spun by the British National Party. Precisely the same issues surrounded student members of the National Front in the 1980s, ending messily and expensively in the courts. Nothing would suit the BNP better than for that outcome to be repeated, as it almost certainly will be if a teaching boycott proceeds.
Extremist organisations thrive on the publicity that goes with the creation of "martyrs" such as Patrick Harrington, the subject of the last big dispute. Universities have procedures for removing students when there is evidence of racism or violence. To act instead on party membership or the possession of objectionable views is doomed to failure and at odds with the principles that the activists claim to defend.