I have it on very good authority that there is another story back.
Everyone keeps going on about the MEW rumour (Marco, Enemy, Web) and how only 2/3rds were released.
The latest speculation I've seen on "Marco" is this--
Gatiss has said that there's a restaging of a scene from "Marco" in An Adventure in Space and Time
. Because of that, they're holding "Marco" back so that AAiSaT
I don't know. That seems like a bit of stretch to me. I don't see the BBC holding back something like "Marco" which is worth money just because of a one-off television film that they haven't even marketed.