The difficulty is that licensed premises are a very defined sector. They sell alcohol, for consumption on-site, and very little else. Anything else they do (food, entertainment etc) is driven aroiund their core purpose of selling alcohol on premises. So its a very easy sector to define whether or not there is a competition issue. With the brewers it was doubly the case, as they were not only limiting places of consumption, but also the products that could be consumed there in the first place - an inter-linked double monopoly. In addition, licensed premises are legally restricted due to a perception of issues re societal impact, whereas supermarkets/convenience stores aren't.
With the likes of Sainsburys and Tescos etc, the problem is defining what particular market they're in. If you take the entire convenience and grocery sector, they wouldn't have a monopoly position as they are up against tens of thousands of small shops, petrol stations, vending machines etc etc. They are even further from being monopoly providers in a number of categories WITHIN their core operation - e.g. toiletries, where Boots and Superdrugs are also big competitors. And then there's other categories where they're nowhere near monopoly providers at all : electronics, homeware, clothing, petrol etc etc. So the problem is, what particular part of the big supermarket's operations would you focus on to try to claim they were collectively monopoly providers, how would that narrow specification be justified, and would it with-stand legal challenge ?
It's a very tricky issue to frame and then tackle.
