Speaking from my own experience (I'm not sure if other trusts have the same procedures), after they accepted my application, I was asked to attend an assessment, which lasted a 1/2 day. This consisted of:
A written exam (you will be sent materials to learn beforehand)
A short driving test (you need to have a driving licence)
A lifting assessment (I would recommend going to the gym and building some upper body strength - they won't accept you if you can't lift a certain weight - can't remember what it is now)
An interview
You have to pass all of these in order for them to take your application forward.