Some providers have always been metered - like Metronet (taken over by Plusnet) who had a low entry cost 300 MB inclusive then pay for extra MB model. Others have had limits for some years.
Standalone small ISPs generally can't sustain the unmetered model if using BT infrastructure as a handful of itinerant internet archivers will seek them out and kill the service with demand.
So "unmetered" is the territory of local loop unbundlers and (perhaps more importantly) ISPs that can attract a wide cross section of the population and not just a few download addicts with the same cumulative demand.
MaxDSL - goes as fast as it can and doesn't read the line checker first.