Hi Ric. I'd say the above postings are very sensible and I'll probably repeat some of the comments here.
Get yourself some good A levels to start with. Then I'd say pick a degree that you'll enjoy rather than necessarily sticking with aviation subjects. Airlines in the UK aren't bothered about the subject matter as long as you have a decent 2:1 and have done plenty of other things with your time at University. You'll also have the option of an alternative career if the flying doesn't work out for any reason.
Make the most of all the opportunities you'll get at University for team work, leadership, etc. and don't forget to have fun! I found that the UAS was great training & really fun but you do need to be seriously interested in the RAF if you're going to consider joining a UAS.
I was a BA cadet. My course was made up of graduates - except one who gave up his Uni course for the cadetship. We had a wide range of degrees, working backgrounds and flying experience (from a trial flight to several hundred hours with the RAF). Those with scientific backgrounds did seem to find the groundschool easier but it isn't a pre-requisite.
Good luck.
[ 23 November 2001: Message edited by: Paddington* ]