Thanks for all your input everyone -
grossgary - doesn't seem to be any torque bind and it's not new to me, I have owned the car for almost 4 years now. Steering and braking have no impact on the noise, it drives me mad because I can literally drive it around for an hour trying to recreate the clunk and it behaves perfectly until I get 50 yards from my house! Other times it will be constant.
I will clean the bearings out at the weekend and check for chips and i'll replace the rear brake pads for good measure. (Oh and i'm in Cyprus so things don't tend to rust very quickly here)
1 Lucky Texan, Mechanically there's nothing broken or loose, I have checked every bush and bolt on the rear end (twice).
I'll take it for a drive later and see if I can't get a recording of the noise - if it co-operates.