Hi Alistair,
If you are interested in becoming a pilot, then being in the ATC is a good start Is your Wing & Squadron approved for BTEC, if so and assuming you reach Staff Part 1 level, then your classifications count towards a BTEC in Aviation Studies (GCSE C Science) level. Also look into the new community service award.
Back to your main question, airline sponsorships are few and far between at the moment and when they do come along competition is extremly tough. I can't see BA re-introducing its cadet scheme in the CURRENT climate. The civil aviation world can be a very strange place with its boom and bust cycles.
Supply (you) for the forseable future will always outstrip requirment (jobs), remember the last time there was a pilot shortage was in 1940-45.
As you are in the ATC take the opportunity to look into a flying career in ANY of the services, but even they are suffering stringent cut-backs at the moment.
I have said many times on this forum that a backup option is essential if you persue the civil route. To this end I strongly advise you in going on to university and take a relevant degree.
While there you can apply for the UAS. Though a degree won't guarantee a sponsorship or a flying job it does open doors to other options.
Best of luck.
RH