"U" is a double album that was first released in 1970. It is the studio version of a stage show they put on with dance troupe Stone Monkey. Apparently there was a plot although you can't tell that from the album - or from the show itself, according to the few who saw it. Possibly one for the fans only, but I'm a fan so I can't judge.
"Queen Of Love" - The Incredible Strong Band
"Puppet Song" - The Incredible String Band
I can't find any clips from the "U" era, but here are the lads a couple of years earlier on the Julie Felix Show. Marvellous stuff.