Hi there,
If you look at the stick thread at the top of this forum you will find pretty much all of the information there. But, to give you a head start go to
www.nats.co.uk and then click on careers. Follow the Air Traffic Controllers links until you reach apply. Then you just need to give a few details and they will give you a date for your first assessments. The rest they will explain via email. You don't need to pay for the NATS course if you are accepted. But I would suggest a lot of research about the job itself before deciding to just 'go for it'.
I hope this helps...