I think the rule about not selling booze to rozzers in uniform is a condition of the license to sell alcohol, not any free-thinking by the retailer.
It will be interesting to see if any more shop assistants start taking the law into their own hands and refusing to serve us. But what hope of a discrimination case being upheld?
Whilst shopping in Sainsbury's in Uxbridge recently wearing blues I was asked by the girl on the checkout "Are you a security guard?". I explained that I was in the RAF. She looked puzzled and did not seem to know of the existence of RAF Uxbridge (all of 1/2 a mile away) nor its attendant uniformed personnel, who are regularly seen out and about the local area in uniform.