With a little help from Simon, handyman-par-excellence, I've got my bike trailer up and running. It's made from two car roof cycle carriers attached to a sawn-off roof rack. This sits on the base of the Carry Freedom trailer (with the extended towing bar) and has a couple of bits of Velcro wrapped around it to hold it rigid, which simply required two one inch long holes cut into the marine ply base.
It's amazingly stable with one or two bikes. It had a real test yesterday as I had six Pedal Power Kennington bikes to donate to a school and it made moving the bikes around more of a joy than a chore.