When I was bringing together the list of questions for this challenge on the British Invaders facebook page I thought I knew the answer for this one already. Nigel Kneale and Rudoph Cartier's adaptation of Orwell's 1984 was one of the gems we discovered doing the podcast. It is still available to watch on the internet but we thought it deserved a DVD release. Then Gordon Iain Aitken pointed out that one already exists.
So instead I turn to another show we covered recently. Doomwatch was a flagship programme for the BBC in the 1970s. It covered important issues in a serious way and is very well remembered. The title has even become a phrase to describe any environmental watchdog. 23 of the original 38 episodes still exist, plus another that was never broadcast. There's a Cult of Doomwatch documentary that would fit well on the DVD extras. I can only presume that some rights problems prevent its release. Maybe Doomwatch.org have the answer.