The problem is that though dogs are not specifically barred from places that serve food, any where that allows dogs on the premises can get only a 1 star in the 'Scores on the Doors' food hygiene system. Few people will want to eat in a place where the food hygiene rating is 'Poor'
The only exception is for guide dogs which are allowed everywhere without the star rating being lowered.
My local 'Weatherspoons' will not allow dogs even at the outside tables as they consider the entire area a 'food service area' I was asked to leave there last week even though my dog was on a lead at the very edge of the outside service area almost in the car park.