As this clip (at the beginning) was filmed in 1973, maybe Commander Straker acquired his desk from some old BBC production, or maybe the clip was filmed at the Harlington-Straker Film Studios. Commander Straker saw it on a set and decided he just liked it. I guess the BBC wondered for ages where it disappeared to little knowing it was eighty feet below them while they were looking... :) Anyway, the rest is history as we know what happened to the desk after 1973 and will into the eighties.
Okay, okay I sometimes let me imagination run wild, but ... well.
NB: As the clip is on the BBC website, I am afraid not you folks will be able to view it. But, there are ways round that :)