How do you mean? Unless I'm missing something, the brands available at service stations are advertised quite prominently on the signs now - eg:
https://goo.gl/maps/LHjejJSRztUASjGH9
They're allowed those signs just before, yes (I
think it's one at one mile and one at 0.5 or something like that). They're not allowed others, which they worked around by creating companies named after the facilities on site which gave rise to these signs. (The intention of the below signs was just to show the operator, i.e. Moto or Welcome Break).
Sign showing "MOTO BK COSTA M&S" etc - from https://www.geograph.org.uk/photo/2460991
However that type of sign is being replaced with ones that list the site name, I can't find a picture of one but it looks a bit like this (I know the distances are wrong!):
Services
Burton-in-Kendal 20
Lancaster (Forton) 35
Tebay 40
This means they can't use that workaround. That said, as I do like to choose one with my preferred brands (in particular I prefer Costa to Starbucks, and if I want a sandwich I prefer M&S Food but if I want some stuff to cook at home I prefer Waitrose) it would actually be useful if they would allow the brands to be properly shown (in those little squares) on the advance signs.
One thing i've just noticed about those signs is the "m" suffix - almost no British road signs other than those have that, it's usually just a number as we already know it's miles.
The other thing that would be useful to add is "between junction X and Y", or "leave at junction X" for one of the "off motorway" official ones, as sometimes you know the junction you're coming off at but not how far it is. This has caught me out when coming off from the M6 to the M54, as there's a services about one mile after the junction.