You are never going to find a British Muslim politician who has been as hard on immigrants as this guy has, and playing the "but Muslim invasion" card on this guy is the worst piece of nonsense you could ever play. Conservatives like him exactly BECAUSE he is the son of an immigrant willing to be hard on immigrants.
Appealing to racist prejudice isn't going to work against this guy. You have to think of something else. This is how Sadiq Khan got elected - racism in Britain is rife, but it is not that overt.