Inevitable in that people in charge of the BBC want to prove that people (specifically an appropriate cross-section of the British public) use the BBC to keep the funding secure
I definitely did not work at an ISP. But what I said doesn't require a static IP per house. Just GeoIP so non-UK residents are treated differently (unless they VPN).
The target is not to determine whether the client is in the UK, but whether the client is a specific license-payer or at a specific address. GeoIP doesn't help to get either of those datapoints.