Mellotronists

There is a track on BJH guitarist John Lees' solo lp A MAJOR FANCY 
credited with tron(played by one Wally Waller).The track is called 
"Untitled No.3" but the sound is one I have never heard.It appears to 
be female voices doing OOOOOs instead of AHHHHs. Was this part of the 
Streetly library(Martin?) I never have heard this on any other albums.
                                            Charles