Then that would depend on the individual university that you want to go to.
I know a second tier university where they accept students with sociology into LLBs so long you get the grades.
For places in the top tier universities, English Lit is probably the better choice.
The other thing you would need to bear in mind is out of the 2 A Levels, which one would you get the higher grade in. If you would get similar grades, then I would opt for the stronger A Level for applications to top unis. If you would do better in one A Level over the other, then you might want to consider doing the subject with the higher grade.
If you don't intend to go to an oversubscribed LLB at a top end uni and your grades are similar, then sociology is probably your more favoured choice.
Note: there is nothing stopping you from doing an extra A Level during gap year if you so wish. Having said that still, sociology is not a required subject, so you would still get into all the degree subjects that you would have done if you did English Lit instead of Sociology. The only minor difference is that you can get into some of the pickier universities and do English degrees with an English Lit A Level, although it's not strictly required for all English degrees at all other universities.
Having said that, I haven't (and would not consider) studied law, so I am not the best person to opine your UCAS application.