On side two at 11:55 Mike Oldfield 'plays' Piltdown Man
Piltdown man - The 'caveman' vocals that are on part two at 11:55. Mike had recorded all the instruments on this section, but thought it needed something more...just nobody was sure quite what. As a crazy idea had after drinking rather a lot of whisky down at the pub local to The Manor (according to one interview...another says that Mike found the whisky in the cellar of The Manor), they ran the tape at a lower speed while Mike shouted and screamed drunkenly into the microphone. With this, the caveman was born. Piltdown man refers to a famous archaeological hoax done with parts of human and monkey skulls put together, which were claimed to be the 'missing link' between man and ape.
From
http://tubular.net/discography/TubularBells.shtml