There should be someone at your school/college who can advise you on this. This is a primarily American site and the contributors are not that familiar with our system.
You say your problem in biology is because of your teacher. Do they teach A level? Does your school have a 6th form or will you be going to 6th form college? Even if your school has a 6th form you don't have to go there.
My gut instinct would to say take biology, but talk to a careers advisor. Write to Harper Adams, their requirement may just be a 2.2 in any degree, but it might not be preferable, and you won't be the only applicant.