It's a little bit complicated but before 1991-1994 (where there are large-scale changes outside of BBC), Radio Times were exclusively for the BBC while TV Times were exclusively for the ITV companies (yes, ITV wasn't just a single company those days!), Channel 4, and S4C (technically there is a third one, Channel Times, but that's for the Channel Islands which has a very interesting ITV setup at that time).
Yeah -- I remember more than a full decade of two listings magazines per week!
To break it down a little for non-British HNers (it is very confusing and messy):
The BBC does not run adverts, but it does have a carve-out from that to mention its own associated products in limited circumstances. Most significantly the listings magazine, The Radio Times.
We start out in the situation zinekeller mentions where the BBC listed BBC TV/radio channels in The Radio Times, and TV Times listed programmes from the ITA (Independent Television Association - ITV/C4/S4C/London Weekend Television etc.)
But then you get a situation where TV viewers are buying two increasingly competitive magazines each week just to get the full listings. As satellite and cable TV appears, this becomes unfair on the consumer (to the benefit of the BBC) and it has to change.
The disclaimer came in part from those publications seeking and being granted access to the listings data that the others were publishing. TV Times got access to BBC listing data, and Radio Times published the ITA channel listings.
But the BBC was and still is able to mention the Radio Times, whereas TV Times cannot advertise on the BBC. A market distortion.
I suppose there must have been calls to ask the BBC to get out of the listings magazine market (I don't remember anything specific) but ultimately the disclaimer ("Other listings magazines are available") was imposed on the BBC.
I should correct myself above because the group wasn't the ITA, it was the ITCA -- the Independent Television Companies Association. Which is now UKIB:
