Easy.
Must have 1000 hours total
Apply to CAA. They look at number of examiners already in your area. If there is room, you can move on. If there are enough, you get nowhere.
If CAA says yes you go and do a two day course with a FIE, followed by a mock PPL skill test with said FIE where you play the examiner.
At some point you need to pay the CAA some money. Can't remember the exact amount, but it will be in the CAA scheme of charges on their website. The authorisation you get is valid for three years.
It's different from the AME debate in that you cannot do the course if there is no space available in your area.
I suggest you get a copy of LASORS or download it from the CAA web site. All this kind of information is in there. It's a very handy reference manual and only costs £10.
Cheers
Gerard