I have an update!
In summary: it looks like we are fixed, but have a new issue
Our MDS on-site visit happened this week. We were pleased that unlike last year's experience, the engineer listened to our explanation and theory of the problem.
He replaced the gas meter, remarking that it was not of a type he'd seen before. He then replaced the electricity meter and comms hub. This meter did not work, so he replaced it with another. The new comms hub is dual-band, though he was concerned that the configuration of our house meant that it was just on the edge of dual-band capabilities. He said that Alt-HAN was not an option in Scotland since its trial use was only taking place in the south.
According to the IHD, all communications have been established, and readings are now visible on the display.
Now the new issue: i thought I'd see what the Bright app showed and was pleased to see that it now had readings for electricity and gas. However... the hourly gas usage on the afternoon that the meter work took place is given as:
0.0, 0.0, 1.63, 0.68, 7,427.67, 0.2, 4.16 KWH.
I'm now looking for advice as to how to address the crazy reading before we get a bill for it! WIll the customer support folks be able to access this info? @Han_EONNext
Thanks all for your help throughout.