[TIGHazard]

Why would the BBC have any control over the Sky and ITV versions? It'd be like Disney having control of all of Doctor Who outside the UK and Ireland - which they don't. Also, what's SGM? I think you mean MGM, or rather it's parent company, Amazon?

I could be completely making this up, but I'm sure I've heard of situations before - in America, in regards to syndication - where an older show (or older episodes in regards to a long running one) isn't allowed to be aired around the timeslot of newer episodes / a remake, to stop audience confusion.

Never heard of that happening over here, but in this particular case it would be MGM refusing to sell repeat rights to Sky while the BBC version is airing. Theoretically the BBC could request MGM to not do so if they wanted, though MGM would not have to abide by that request.