There are load of hoops you have to jump through before you apply to the ATP scheme: the first thing you need is your licence issued!!!!
then you will need a basic disclosure certificate, 3 passport photos, a reference from your flying school or college, and satisfactory completion of a form with a lot of white spaces on it. Oh, and you'll need £4K or so burning a hole in your pocket for their AQC course (which is like an MCC course plus a bit).