Landing, with your A levels I can nearly see myself 20ish years ago!
, I didn't go to Uni but can see your logic for choice of course. However, Genghis' advice in my opinion is very good, if one were to be harsh, ask yourself how history would work in the context of 'career' in aviation. Its easier to find a logical link between modern languages and geography for example, but not so easily for history per se.
You mention that due to medical 'issues' you may not be able to be a pilot, just as a heads up, that may preclude some elements of a career in ATC for example, particularly if aiming for a controllers position, so you may need to bear that in mind. So I'd steer more towards a degree with a potential 'link' to aviation rather than history, which whilst proving the ability to learn, may be limited in helping getting the foot in the door.
Check also some of the uni's for aviation related degrees, City University used to do a foundation degree in Aviation Management, try Cranfield Beds as well. I do suspect that as others have indicated there will be a bias towards numeracy as part of the core subject. If you're more biased towards the arts, perhaps a marketing/
PR slant might work for you, its a realtively small field but would also be 'transferrable' to other industries. Transferrable degrees/talents will become even more usefull in the future, one downside of aviation is that sometimes you could end up too specialised!.
As for part time work, generally it won't pay particularly well, local flying clubs might need a 'hanger rat' in the summer, or some handling agents at big airports take ground handling/ops staff, for the airport jobs, you might be age restricted, and you'll need a clean 'crim' sheet to work airside. It would be good experience though, and might help formulate your career ideas further.
PS: also have a quick look at G's post on the interview thread on this forum!