Judge Death wrote:
If there was someone out there with a huge stash, what would stop them cutting out the middle man, as it were, and just making a deal with a DVD production company? Or are the episodes still effectively BBC copyright material (even though the BBC effectively destroyed all copies back in the day).
The BBC owns the copyright on the material on the films. There's no way to commercially exploit it without the BBC's participation.
And even if the person who had the hoard waited for the copyrights to expire in a few decades, the BBC could attempt to stifle exploitation through trademark.