Clarify whether or not it would be a qualifying law degree. If it would, and you'd be interested in the sociology modules, go for it. But I get the feeling that you wouldn't necessarily, given that you applied for solely the LLB in the first place. Leicester is still a really good uni - OK, not as good an institution as Warwick but nonetheless, still good. If you do really well there and work really hard, doing the course YOU want to do and potentially ending up where you want to, go there. It also depends on whether you actually like Leicester as a uni and can imagine yourself there: in cases like this, it's always best to actually visit and see how you feel.