"In the 1970s there were no cities with "computer optimised" traffic management, I refer the honourable gentleman to the 1969 film, The Italian Job "
My learned friend will not mind being reminded that we're talking about the UK, and that the traffic system in question was not (the hint is in the title). Perhaps "*very few* British cities had "computer optimised" traffic management" would be better. Look up SCOOT from the TRRL (pioneered in the 1990s).
"card transactions ... paper... absolutely no difference at all if there's no power."
Yes and no. Vastly more card transactions these days, and many (most?) card transactions *require* online authentication. Without on-line authentication, business is greatly disrupted.
"many cellular sites have some amount of battery and/or generator backup (the bigger sites anyway),"
As you say, typically this is bigger sites. In many parts of the UK, coverage and capacity are only adequate because of small lower power cells which don't have any meaningful battery backup.
"If you have a wired phone, chances are that it will work through a power cut."
If it's routed through BT equipment in a BT exchange, probably.
If it's a cable phone? Don't count on it.
If it's LLU voice? Don't know, could guess, would prefer definitive info.
We'll find out soon enough.