Thanks Julian, I have been down to my local bearing dist. They confirmed what you have said, the key number is '6204'. This number is recognized by all the key quality manufacturers. They also checked out the Hoffmann 120 number, as in the BSA W/S Manual, this refers straight back to RHP 6204, who bought out Hoffmann.
So the only query that I now have is my Spindle? Is there only one type? Do the smaller bikes with Conical Hubs have a different spindle? OR is there only one type?
Bruce.