Thanks Broomstick.
Yes they looked into BPPV early on into this (over two years ago) but that's not the problem. My left (inner) ear is all buggered up. Way too sensitive, in fact 40% more sensitive to movement than the right.
This is measured during a VNG test where they pour water in your ears while wearing dark goggles, then they measure your eyes response to the stimulation of the ear. Its not pleasant.
Incidentally, i'm 47 years old in perfect health otherwise.