can you join RAF police with past history of anorexia nervosa?

If the British Army wouldn't allow you to enroll, the RAF more than likely won't you to enroll either. More troubling is your history of repeated interest in cocaine usage - "how many lines a week make an addict", etc. Your possible and more than likely cocaine usage is more of a block to enrollment than your past mental health issues related to your diet.

Besides that, you might be too old for active service as you're relating issues that usually occur in late teen age or young adult years as being TEN years ago.