You want a job in the meantime which will eanble you to save yet will provide you with useful life experience for the airline interview. If I was 18 again, I'd look closely at becoming a railway signaller. You get paid over 75% of your final salary during training (approx 1 year) so if you're in a complex signal box you're looking at over £30k year before you're even productive. Lots of overtime opportunities once you're qualified you should be able to smash a grand a month into a savings account even if you're living away from home.. It's a very good career on it's own, the the smaller boxes are facing redundancies due to everything being moved to the ROCs.
The railway is generally good with salaries and overtime, a platform dislatcher can make well north of £30k with a bit of overtime. The Merchant Navy is good too, minimal living expenses, relatively little tax once you're qualified and plenty of time to study. Sales careers can be good earners if that's something you're good at (I'm not), I do think you need to be a certain "type" to succeed in sales.
Bear in mind, shift work and safety critical jobs are both relevant to the pilot role, if you've had an interesting job prior to pilot training, it does make you a more interesting candidate at interview.