Okay ... that was seriously fucking weird!
Gelgud also did a movie version of the Tempest where virtually every character was naked at some point.
I suspect we are talking about the same film. There was a very recent one with Helen Mirren cast as Prospero, but Gielgud was not in it. Also, I do not recall nudity, though there may have been some in the Tempest with Gielgud. The title of the Gielgud was "Prospero's Books." They used attractive actors for the scenes, but did not concentrate on close shots of their faces because Gielgud was reading all of their lines. This allowed Peter Greenaway, the director, to establish a visual sense that was astonishing and unique. I love the film. Gielgud is tremendous in it.
It was this 1991 version
Actually it contained more naked people than most any other film, but was not at all sexual. The nudity superbly was woven in to create an unearthly, magical aura to the setting. It was treated as a completely normal part of life (perhaps why it was well liked by naturists)
A little weird but I enjoyed the video.