Well, i am chuffed to nuts right now, having endured an ongoing problem with clanking forks, i have finally fixed them thanks to MikeN. The problem was the tapered prong contacting with the side of the hole in the bottom nut on the stanchion. the hole seemed not to be central to the prong as it was contacting on one side of the hole only, also, with the fork bottomed out (and off the bike) i could feel resistance on and off when i rotated the slider in relation to the leg. I then carefully removed material from the inside of the hole with a round file until it rotated freely.
I have just been for a test ride and this time i was actually looking for sunken drain covers etc rather than avoiding them, as the bike bumps silently over them now, the ride is hugely improved!
I don`t know how long it would have taken me to figure it out if it had not been for this forum`s knowledgeable members, so thanks Mike and everyone else for their input
Richie
p.s. Chris, hopefully this will help you with your problem (fingers crossed)