sorry, if I am correct you are asking should you do A2 eng lit, in addition to maths, chem and bio A2.
If so; I would say no, unless you are desperate to do english lit. For Oxon and Imperial the bmat and interview are both miles more important than collecting qualifications. No medical school cares about 4 A2 levels, and you would be better off focusing on your 3 A2 levels, interviews, admissions tests and just having a bit of fun.
I may have the wrong end of the stick, it seems quite a confusing situation!