hi
check with BALPA (BRITISH AIRLINE PILOTS ASSOCIAtION) i saw something advertised for people starting out on training that they could get insurance with them in case they loss their medical. i was interested cos i am in same boat as you .i think you might have to join and this is was put me off , it might come against me in applying for the likes of ryanair who dont want you joined any unions.
cheers