Here is an in-depth article about the kinds of people pushing this behaviour forward.
Twitter of the owner. At least they seem to not be backing down. From what I’ve seen there’s nothing in their history that is anti-Semitic, only pro-Palestine and anti-Israel. Yet the framing of the issue by news media is consistently calling them racist, anti-Semitic etc. Fuck Toronto Sun.
Combination of that and being physically at a number of events with Hamas and other groups that could be used as fodder for him "loving terrorists". This was mainly effective because of his IRA work and support. Regardless of our views on the IRA in the left they are viewed very negatively in the UK basically everyone except the extremely informed left, it was baggage easily leveraged against him.