Maybe more obvious
It wouldn't surprise me if part of the deal the BBC made with smart tv makers was that to include the iPlayer app, they had to send additional details to the BBC either directly from the app or from their own telemetrics data received from the tv.
So the unique tv name or licence and/or MAC address.
If they have the MAC address and the tv is wireless, the detector vans only need do a simple monitor of the wifi in the area to see which devices connect to each other to determine TV and router combination. From there, it's easy to narrow down what house a router is in by it's signal.
You can do exactly the same with the usual wifi hacking tools and an app on your android phone that gets beeps more intense as you get close to the router/the signal gets stronger.
Biting the hand that feeds IT
