So this is going to be me exposing my own stupidity I'm sure, but what is the actual reason why the utility company can't measure how much I use and then bill me for that, rather than the somewhat baroque approaches they use?So this is going to be me exposing my own stupidity I'm sure, but what is the actual reason why the utility company can't measure how much I use and then bill me for that, rather than the somewhat baroque approaches they use?

I think they can but in theory the recommended/ preferred method is to estimate annual use and "smooth" the payments through the year.

They can - you can switch to a variable direct debit. But for most people/households this is too confusing, or it leads to too many failed payments, so the norm is to try to even it out across the year.