Dave, I have a towbar mounted carrier out in the garage. I have not used it for a few years but it is in good working order, certainly in need of a clean. I have been meaning to advertise it "somewhere" for a while but the potential cost of packing and posting it has been the main issue stopping me. I'm not sure what make it is but I'll have a look if you are interested...
(edit - it's one of the ones after the "spare clamps" but not sure what model as I have not gone out to the garage yet and not even certain that I'll know even then. But not for a Land Rover!:
http://www.wilmond.co.uk/acatalog/Cycle_Carriers.html)