I'm Scottish so don't fully understand the English system (they're way different)
COMPULSORY SUBJECTS: Maths, English(Communications), 1 Foreign Language subject, Physical Education
OPTIONAL: Physics, Electronics(Technical Education), Technical- woodwork/metalwork, Computing
Like I said before, drop READING UNIVERSITY an email or phone them, they wont always have time to talk but usually educational institutes are happy to talk for a few minutes.
Another option is looking at Reading University's prospectus for their robotics course and copying the entry requirements. Then do a search for college's (do they call them that in England?)in your area, look for the entry requirements for the courses you'll need for the robotics course. Choose these as your courses in your secondary school.
In Scotland we had/have people called 'Guidance Councilor's' , they're there to help you with these kind of decisions. You can call in at the front desk and ask to make an appointment with them. If you're not close to choosing your subjects they'll probably make an appointment for just after school finishes or during your lunchbreak. They'll even help a bit with finding things out etc.
Hope that made sense (It does in my head