I managed it.  I got the gold card working by

• making a new one (which did not work at first);
• formatting it using the phone itself (not the card reader);
• rebooting by taking out the battery for a few seconds;
• switching on USB debugging in Menu > Settings > Applications > Development.  I have no idea which of these was the critical one.

I now have a working phone on the latest HTC build and am checking that everything is operating properly.  It is OK so far and google immediately reinstalled all the apps I had downloaded.  I have hooked up various accounts and it is now just a question of remembering which icons went where.

Now I have managed this trick, I wonder about whether I will ever need the gold card again?  Has the phone now fully escaped from its orange branding or is the Carrier ID still an Orange one?  There is so little information about gold cards on the internet.

Later:  Found out from android forums that the phone has not escaped from Orange at all, and I should make my standard sd card in to a gold card.  I will try that, but I won’t know if it is working until I try to do an Over The Air (OTA) update…