Ahem ...
Before you start using the term "tinfoil hat conspiracy theorists" as an easy way to dismiss someone without bothering with "inconvenient but true small details" you should maybe take into account this joke (or maybe not really a joke?):
"-- What's the difference between a conspiracy theory and confirmed facts?
-- Currently 6 months, and shrinking ..."
I was also harassed regularly about "be smart and get a smart meter".
When they switched to new tactics and send me a letter saying my meter is outdated and needs urgently to be replaced, I took the serial number of the meter and when searching online. Turned out that meters do have to be ‘certified’ and the certification is not for ever. No doubts about it.
Only thing is, when I checked on the manufacturer’s website and then on the OFGEM’s site https://www.ofgem.gov.uk it showed my meter is still certified for several more years, and is certainly NOT 'due to be immediately replaced'. So instead of booking an urgent appointment, I phone them back and threatened to sue them for harassment. They had a recent decision by the energy Ombudsman about another dispute to figure out if I meant it or not.
Never heard anything about "be smart …" since.
Even if the meter is past its certification date, there are still companies/manufacturers that will supply and/or install a new plain meter.