LG&F
The fail your fitness test was not meant to be serious... although my favourite way out of the forces was taken by film actor David Niven. He was a career officer in the Highland light Infantry in the 1930s (I use the word career loosely). He was under house arrest following some misdemeanour during a machine gun course: he escaped from the mess by getting his escorting officer drunk; ran away to Hollywood to become an actor and sent the immortal telegram back to the UK, "Dear Colonel, Request permission to resign commission. Love Niven." he was successful. Mind you, he returned to UK when WW2 broke out and re-gained a commission in the Rifle Corps. He commanded the SAS "Phantom" net for a while and ended the war as a Lt Col.
If you get the chance, read "The Moon's a Balloon" - its a good read.