The UAS is an excellent place to start. As I understand it, you will do well to receive a 3 year sponsorship, but may be awarded one later on in your university carreer/jolly.
At Officer and Aircrew Selection (can't remember the new name for it - long time ago for me!), I'd advise a bit of quiet arrogance, and tell them that you're joining to be a pilot, and pilot only. If you put down other brances that you'd accept, the danger is that if you're a borderline case, they might take the easy option of sending you to the RAF Regt (fine fellows, of course) or whatever. It also shows some drive, and an unwillingness to take second best (no offence, navs etc).
Nowadays, you're assessed for your future pilot ability at UAS, and while the RAF will tell you that your degree comes first, your future aircraft type depends on how well you perform in the air at UAS. Don't let this deter you, but be advised, to get the best degree you can (which you MUST do) and to fly as well as you can will require self-discipline and hard work.
Note, above all, that the UAS is a fantastic opportunity, and arguably the best way to join up as aircrew. You will love university life and the UAS.
Get stuck in!