An interesting question, vetuste_ennemi, and a helpful link.
The APPG definition is a bit of a mess, conflating different ideas into one bullet point. I am in favour of an independent Palestine, for example, but against theocratic government, and any thoughts I have on terrorism are unrelated to either belief.
One issue is that a separate definition for each minority group can easily become unwieldy. I already had reservations about the examples included in the antisemitism definition, as it opens up a whole new debate about whether the spirit or the letter of the law is central to its purpose.
I favour a single definition of what specifically constitutes mistreatment of a minority but is not already covered by existing legislation. We have equal rights laws, anti-discrimination laws, hate speech laws, but having too many can hamper justice. On a superficial level, more laws means more loopholes, but there is a deeper shortcoming in that the CPS have been condemned in some instances for prosecuting under the 'wrong' law. Another example is the decision to try the Stansted protestors under a law designed to be used against terrorists. Perhaps they would have received harsher sentences for aggravated trespass, because they would likely have pleaded guilty and saved the nation a big wad of cash and court time. I don't think most people realise how much time is wasted sitting around while solicitors or barristers are stuck in a different hearing in the same building.
I would rather the UK stayed in the EU, but leaving might be an opportunity to revise all our laws so they are less dependent on sections and amendments to older statutes, and trimming them down to lose the excess words. A killing is a killing and should be tried as such. Political, religious, ethnic and other supposed justifications can be dealt with as mitigating circumstances, without needing a law of their own.