Having re-read this thread, the forum Members who posted about this brake failure on start-up now number a total of 8 including myself. Rather a large number for a relatively small membership. They are:
BigT (thread starter), PeteS, BeckyDuck101, blythpower, Daffodil, Chris52, Cobb2, and most recently me.
I am waiting for my Jazz to be recovered today by the AA (part of the "discretionary" Honda Care service) and delivered to Bath Honda this afternoon. Update to follow when I have more information.
I suggest that anyone else who experiences this failure and the accompanying cascade of dash warning symbols and bleeps, records it on their smartphone, just in case their dealership finds the fault has fixed itself. I have made such a video in case of a dispute.