This is true of many of the Canterbury bands (like Henry Cow), but some Canterburians lean more toward progressive rock (Caravan) and some more toward avant garde / experimental (Fred Frith). Soft Machine tends to fit between these two poles, especially their third and fourth albums, as does Kevin Ayers and the Whole World's album "Shooting at the Moon," with some experimental works and some straightforward proggy songs.

Soft Machine, "Teeth": https://youtu.be/WpOLIQNuekc

Kevin Ayers and the Whole World, "Pisser dans un violon": https://youtu.be/x372e5wPAH0

Kevin Ayers and the Whole World, "May I"? https://youtu.be/smVIHvV2a9o

There's also the related RIO (Rock in Opposition) movement, which tends to be more experimental (Henry Cow, Art Bears, Magma).

A fine intro.