Oh, yes I do. Great memories. Derek Sarjeant probably knows more about all 3 than anybody else I can think of.
They all used to appear regularly at Derek's Surbiton Folk Club in the 60s, where I was one of the junior residents. I also remember John playing 2 whistles at the same time, one up each nostril. And doing somersaults off the top of the piano (pre-dating Otway by years). But, at the same time he was a fine guitarist and singer, and wrote some good serious songs as well as the funny stuff. Also got signed up by the Beatles' Apple organisation in the 60s, but nothing came of it.
Pat Nelson was a real gentleman,more at the Country end of things. (In fact I have a feeling he may have guest-presented 'Country Meets Folk' on BBC Radio). He certainly had a regular show on both TV and Radio on the South Coast. I even got to play a bit of guitar on one of his records once!
Diz, of course, is a legend in the true sense. He's not playing anymore, but is still going reasonably strong (Last I heard) after a a bit of trouble with the old ticker in the past couple of years. He'll be 78 this year. In the late 60s and early 70s, he single-handedly regenerated the career of Stephane Grapelli, who was distinctly unfashionable at that point. Recreating the old Hot Club repertoire, with Diz in the role of Django, they went on to become one of the 'hottest' acts on the planet, touring concert halls all over the World. And surely everybody remembers that performance on Parkinson when Grapelli wiped the floor with Yehudi Menuhin, with Diz in the background with the band, clowning around just as he always did. Diz always did the folk clubs, and for years was the biggest crowd puller bar none.

Graham