I very much doubt that an in-depth knowledge of English, History or Politics would be seen as essential for studying law. (I fail to see any any direct relevance to Law for the poetry of W.B.Yeats. I can't think of any reason why a knowledge of the rise and fall of the Austro-Hungarian empire should help. Even a knowledge of political systems doesn't help with an understanding of the application of the laws passed by politicians).
The one A-level subject which might be of most relevance is, of course, Law but if your school or college doesn't include it as an option, there's not much you can do about that. (Even so, I suspect that many university lecturers would prefer their students to arrive unburdened by the A-level Law syllabus).
Two other A-levels which might be relevant are Maths (because of the need for clear, logical, structured and coherent thought) and Business Studies (to provide a knowledge of the way that the law is applied in commerce). So your current subject choices might be fine.
Many universities now require candidates for admission to law courses to take the LNAT. (This is in addition to achieving high grades in their chosen A-level subjects). These universities include most of the 'prestigious' universities for law degrees, such as Oxford, Cambridge, UCL, KCL and Durham. It's likely that, as long as your A-level grades are high enough, the universities would give greater weight to your performance in the LNAT than to your choice of A-level subjects.
Information about the LNAT is here:
http://www.lnat.ac.uk/
I suggest that you work through the links, down the right hand side, to check each university's individual requirements for admission to study law.
Chris