Having read the advice in post 62 (thanks again Louis), what happens if the car is not road registered and/or has only a bill of sale as proof of ownership, but is being towed by a private individual? Also whilst spares and consumables must be listed for the vehicle, what about tools?
Just did a quick search and found this company
https://www.ata-carnet.uk/eu/. There are others including the Birmingham CoC, so I may try to determine the costs for my MG to use as an example.