Apparently not!
I got this from the Food Standards Agency:
Businesses in England and Northern Ireland do not have to display their rating. So if you see a business without a hygiene rating sticker or certificate, you’ll have to decide if you want to eat or buy food from there without knowing the hygiene standards.
Putting a hygiene rating on show is a good advertisement for businesses that meet the requirements of food hygiene law.
A good food hygiene rating is good for business.
The situation is different in Wales. Businesses that get a new rating after 28 November 2013, must by law display a sticker showing their rating in a prominent place in all entrances to the premises.
- See more at:
https://www.food.gov.uk/multimedia/hygiene-rating-schemes/ratings-find-out-more-en/fhrs#sthash.FTaFWfAr.dpuf
I suppose the rule to follow is this:
If you don't see a sticker..walk on by.