Strictly speaking, This is not a "BBC Session", because it is a "studio live show as you can hear. Also you can hear, DJ (John Peel) say "YES will be playing Queen Elizabeth Hall this coming Saturday". And The Queen Elizabeth Hall gig was actually on Saturday Mar. 21 '70!!
I would add that "Disillusion" from "Starship Trooper" was actually taken from a song of Chris' called "For Everyone". This demonstrates one of Yes' great talents: the ability to take music from different writers and make it into something stronger through the collaboration of band members. Yes music is so much better than just the sum of the parts. It's the fact that a guitarist who is inclined toward finger-picking slapped his style of playing onto the bassist's existing rock composition that drives it to levels unreachable by most rock bands.