Success! Many thanks for the help Tim, I stopped by my LBS on the way home tonight and got cone spanners, a 10mm allen key, some degreaser and teflon lube. After pulling the hub apart, cleaning it and relubing it, it now works like a charm. The only slight concern is that the freehub body sounds like there's metal rubbing on metal inside it, like there's not enough grease inside. So, can someone tell me please, where should a freehub body be greased, and how much is required?
Many thanks
Mark