Personally, repeating the advice I gave earlier, I would get a diagnostic done with the proper Honda dealer diagnostic kit, before you do anything. Otherwise, you are just stabbing in the dark.
I don't know which diagnostic tool the AA use, some of the generic tools used by garages are very good and can connect to multple systems on the car, but nothing beats the dealer tool for diagnostics. "Test not successful" for the rear sensors is very vague, and does not point you to any particular fault - it sounds more like the diagnostic tool used was unable to complete the test for some reason.
You mentioned earlier that it was affected by road humps. It would be worth checking all of the ABS sensor connectors and wiring at the wheels, particularly the flexible cables on the front axle, and the rears where they flex at the beam axle. Look for any splits or cracks in the outer sheath. It might save you the cost of a diagnostic.
