With regards to the Army, you can fly as either an officer or as an NCO.
As an officer you would apply to join the Army Air Corps during your training at Sandhurst. Should the AAC accept you, and you can pass the aircrew selection/medical, then you would attend the Army pilots course. However, should you fail the course, the AAC has no further use for you and you would have to leave the Army or transfer to another Regiment. Alternativly you could join another Regiment initially, and then apply for pilot training after a year or so. That way if you fail, you have a job to go back to. The downside of that route is that some Regiments consider it as bad form to want to leave them to do something else.
To fly as an NCO, you join as a private soldier either direct to the AAC or as above, to another Regiment. Having reached the rank of Corporal, then you can apply to be a pilot. Should you join the AAC and fail, then unlike the officer, you still have a job to go back to.
The officer route requires the necessary qualifications for Sandhurst as well as the ability to fly. The NCO route doesn't require any formal quals. As long as you can pass the aptitude tests and the medical then you can have ago. Officers tend to fly less than the NCOs after the first couple of years as more of their time gets taken up with desk jobs and ground tours. As an NCO you could get 10 - 15 years of flying. So you pays your money and takes your choice.
Whatever you choose, good luck and enjoy it.
[This message has been edited by MightyGem (edited 29 July 2000).]