RAF Aircrew - Any history of Asthma ZERO chance. Full Stop. Period. I was binned from even flying the Vigilant, the Air cadet glider when they found out. Sorry to give you bad news but don't waste your time.
HOWEVER, the CAA don't see this as such a big problem, and I have a full class 1 medical for flying so a civvy career in flying is very much possible.
Shaft