The programme doesn't seem to be on iPlayer so I can't check this, but if the Britten piece was for solo guitar, that will have been the Nocturnal. Written in 1964 it's one of the pinnacles of late 20C classical guitar. The piece is a set of variations on Dowland's Come, Heavy Sleep, finishing of with a reworking of the theme, rather than starting with it. From the cacophony description it was probably the Passacaglia, which is relatively long and rambling, based on a short descending motif from the Dowland song. The piece does have some more lyrical sections - the opening variation for instance, and the final movement which is a harmonisation the Dowland song is particularly beautiful.

(The footage of him playing the Passacaglia appears on the Music On Earth video of Julian Bream - My Life in Music. The video is well worth getting if you are interested in his life and playing. The same people also did a wonderful video on the life of Stephane Grappelli - A Life In The Jazz Century.)

Mick

(hoping, after all that, that it was the Nocturnal!).