Dear Clive It's a good point you raise. I would hope the BBC could check again to see if they have the whole clip. Also; it's such a shame that the colour copy that German show "Disco 73" have runs at under 2 minutes - a great pity! ASM
I think the clip used in the Promo video was intentionally shown in B&W to match the style of the rest of the promo, the original colour clip has lots of solorisation on it which I guess the director of the 1991 promo wanted to avoid.
I guess they did use the short 'Disco' version as towards the end of the promo they switch to using another (possibly European) tv performance of Bolan singing '20th Century Boy'