IMHO, you would have to be bonkers not to take some sort of biology now - not for reasons of having more schools open to you, but becuase you WILL have to bring yourself upto A-Level standard yourself either before the course starts or during your pre-clinical.
There is no real way around it, as others have said the teaching of pre-clinical medicine is probably more biology based than anything else - the reason that chem is usually more of a requirement is that all med schools will have the staff on hand to help with remedial biology, but not necessarily with chemistry - as demonstrated by the number of universities who have 'lost' their chem departments over the last 10 years.
If you want o make med school a little easier, and free up more pre-clinical time for fun, rather than self-directed study, then do some biology now.
===**This has been a 'biology is helpful broadcast' on behalf of Fluffy, who is tired**===