The link before Hawkwind was the one I thought might be the hardest as this person only guested with Hawkwind on a tour or maybe two. I saw them together at the Canterbury festival a couple of years ago and they did 'Silver Machine' together.

As a clue, Carl Palmer used to be a member of his band before ELP but CP isn't the person I was looking for but thinking about it CP would fit the chain too.....another clue there.....this should steer you in the right direction.