I found that a Physics A-Level was more than enough to see me through my ATPL Theory of Flight. If you like Aero Eng or can see an alternative career in that discipline then go for it. However, you are better off having a good degree in a subject you enjoy, than a poor degree in Aero Eng.
As for your initial question of whether to do a degree or not, I would say do it. As has been mentioned, the market for pilots is now quite depressed and will hopefully improve by the time you emerge from uni. Most of the airlines who sponsor seem to prefer graduates and even if they do start recruiting for cadets and you get accepted, then you can always drop out of uni. Should the pilot career not work out (and there are reasons beyond your control why it shouldn't) then you will have had a great 3 years and be well qualified to get a proper (ie well-paid!) job.
Finally, and people often forget this on this sort of thread, uni is great fun! 3 or more years of being treated like an adult with none of the responsibilities. You'll make good friends, drink far too much and emerge a much more well-rounded individual than when you went in.