Thanks for the input, guys!
Funny you should mention Rod Slater of the Bonzos. He was in the same flat and actually told me about this guy.
Rod, the tuba player, wasn't a professional, but was a member of the St. Martin's Jazz Band in 1961 alongside Rod Slater. Rod Slater became a Bonzo, and other Rod didn't.
By 1964 or so, Mr. Slater had moved into St. Mary's Terrace where he found the other Rod on the floor below. He can't remember his surname, but I thought that having the address - and names of both Slater and O'Neill as other residents - might help me find my man.
As I'm writing a huge history on the Bonzos' earliest years, knowing Rod the tubist's surname would be a useful addition. Hence the searching!
Hope this is useful. You lot have been