Ben,
Frankly I am amazed and disgusted at the response you've had from NATS, if you were applying for an administrative job and were equally or better qualified than the next candidate but confined to a wheelchair, they would have moved heaven and earth to employ you, purely because they wouldn't have a leg to stand on if they hadn't taken you on.
I wish I could think of a way of helping you further, I don't suppose that any disability rights groups or other such organisations could help you out?
You must be very demorolised, but don't give up, the internet is a very powerful tool, and with any luck a bit of time spent beavering away may be to your ultimate benefit.
All the best.