DS is in a student house-share and none of them watch much TV. If they do watch, it's likely to be on a streaming service such as Netflix. They haven't bought a tv licence. On the very rare occasions when they do want to watch something live or on iplayer they are aware of a loophole (in screenshot) that they understand allows them to watch live tv on unplugged devices (under the protection of their parents' home licenses). Have any of your student children succesfully relied on this loophole when the licence folk come knocking?
This link suggests the bbc can trace viewing habits via IP addresses: https://forums.moneysavingexpert.com/discussion/6201498/tv-licensing-spying-on-home-internet-usage, but I doubt they could tell whether a device is plugged into the wall or not, could they?