Well, Jock, you inspired me to do some research -- usually I'm a master (or is that the Master) Googler, but the key words (canon, 8th Doctor, etc.) mostly turned up a batch of debate and speculation pages. So it wasn't easy.
But I finally -- FINALLY -- found this. I don't think it's the article I was referring to above (unless I misremembered or misinterpreted the specifics after I first read it -- all too possible, alas) but it defined the official word at the time. And clearly it was far more formal an understanding than I postulated in the previous post.
The full article is here:
and the relevant passage is duplicated below:
(Reprinted from DOCTOR WHO MAGAZINE #275)
"To ensure that the plays remain faithful to the Doctor Who TV series in terms of style and content, BBC Worldwide has understandably insisted upon the right to approve all storylines and scripts. To this end, Stephen Cole -- consultant to the Doctor Who book and video ranges at Worldwide -- has been appointed executive producer for the BBC for Big Finish's Doctor Who output.
"Cole commented: 'As for as the BBC is concerned, these new stories are seen as part of the official Doctor Who canon. A great deal of responsibility comes with that status, and Worldwide did not assign this licence without careful thought. I will do everything I can to help Big Finish produce new Doctor Who to the highest possible standard and for the widest possible audience.' "
That established ... a bulletin board poster (at http://www.barbelith.com/topic/20565/from/385),
citing a much more RECENT ish of DWM, said the following, which backs up your stance almost word-for-word.
"There is an interesting bit in this month's DWM by [Russel T. Davis] about how NONE of the external media is allowed to be canon, because the BBC's charter expressly forbids programme makers to create anything that requires viewers/ listeners to buy merchandise (and by this they mean all books/ magazines/ comics/ DVDs/videos/ audio adventures/ yada/ and/ yada) in order to understand a BBC production. It doesn't matter what the McGann novels say, it means nothing in the world off RTD BBC Who."
So it seems we're BOTH right ... Like the Doctor himself, I think the truth has regenerated to fit the circumstance.