Maths is likely to be your biggest shock, to be honest. Not much point reading up on languages (especially somewhat obscure ones that most of your fellow students won't have encountered either) when instead you could do a little revision of your maths skills, make sure you're ready for what they'll throw at you on the course.
Take a look here (2014 data but should be mostly the same):
http://www.kent.ac.uk/courses/undergraduate/124/computer-science#structure
Under stage 1 there are two modules, "Foundations of Computing" I and II (which I would assume are core content!), covering mathematical topics such as set theory, matrices and vectors and differential calculus. A-Level maths covers all of these, so you may find that some of your fellow students already know this material and can cover it quickly, whereas you might not have encountered any of it before.
Take a look here (2014 data but should be mostly the same):
http://www.kent.ac.uk/courses/undergraduate/124/computer-science#structure
Under stage 1 there are two modules, "Foundations of Computing" I and II (which I would assume are core content!), covering mathematical topics such as set theory, matrices and vectors and differential calculus. A-Level maths covers all of these, so you may find that some of your fellow students already know this material and can cover it quickly, whereas you might not have encountered any of it before.