You can see a UK smart meter being taken apart here [1] with the GPRS module shown at around the 2 minute mark. And you can look at meter datasheets [2] which list GPRS WAN as a feature.
Smart meters often send a reading every 30 minutes. Some energy companies will then show a breakdown on their website that purports to show how much you're spending on lighting, fridges, appliances and things like that [3].
I suspect they use a lot of guesswork to arrive at that breakdown, given the limited input data. Although it's probably fairly easy to recognise certain multi-hour-and-distinctively-large loads, like EV charging and heat pumps.
[1] https://www.youtube.com/watch?v=G32NYQpvy8Q [2] https://www.securemeters.com/sea/wp-content/uploads/sites/15... [3] https://imgur.com/a/L0xwWEo
>>However, it's pretty clear the policy intent isn't only to let people monitor their usage.
Of course - but I contest OP's claim that it has enough granularity to tell you that you're showering too much or that your tool shed uses too much energy - it doesn't allow that in the slightest.