Earlier quoted context omitted.
Most of the altnets are not government funded - there was a ridiculous amount of money put in them from the low interest rate period, many many billions. I very much doubt they will get a good return given the crazy level of overbuild going on. I have now 4 separate infrastructure-wise FTTH networks available to me in my London apartment.
I believe (without supporting data) that most altnets that are expanding coverage to people with poor broadband are government funded. The economics in London are quite different than that of a rural village.
Economics aren't actually that different for villages (very rural single dwellings are though of course). Most villages of say 1k ppl already have fibre going to them (for VDSL cabinets), so they can buy the backhaul from Openreach.
Then it's a case of adding the actual fibre which they can use existing telegraph poles for.
There isn't really a huge difference in economics between urban suburbs and villages.
London is actually not as cheap as you'd think, because a lot of properties are apartments and that requires expensive wayleave agreements to be negotiated with the freeholder. This has significantly increased the cost, as many freeholders don't care and don't respond or want a lot of money for the permission, meaning you have to dig up the street regardless and miss a lot of properties and hope they can be added later.
Plus the cost and complexity of closing roads/streets is much higher in London than other areas.