The carrier on the GT K7 is not the standard Suzuki carrier shown in the parts fiches, but part of a Suzuki GB luggage system fitted by Suzuki GB. Suzuki dealers do not have any factory parts info and cannot get spares for them from Suzuki GB. I understand that each model year of the K series GTs had different systems supplied by different luggage manufacturers. The cases on my particular bike are by a company called Soft, but I believe Givi and Hepco & Becker supplied kit in other years.
However, it seems that 10kg is probably the answer to use. That won’t be a problem in that the weights of the NHS boxes are generally less than 10kg, except, as I mentioned above, certain boxes going to a specific hospital. That can be managed quite easily by the logistics controller who can ask me to use my car if a heavier load is necessary.
For my own purposes I’m quite confident the the carrier can safely carry a heavier load and I have indeed carried significantly more than 10kg on my recent 11day trip to Spain and France without any problems at all. But in the matter of official “elf and safety” the rules have to be obeyed!
Anyway, thanks to all for your advice.