If I were to critique / mock the Donald or the Boris in a manner which referenced their appearance, I doubt very much whether I'd face the same barrage of criticism should my chosen target instead have instead been Saint Jeremy. i.e. 'It doesn't matter that it walks like a duck, quacks like a duck...we need to get beyond this...it's a sad reflection on modern politics' etc. etc.
Well, believe it or not, the leader of Her Majesty's opposition has to be more than any old convenient host for a pay-load of policies.