>Interfering with her reception of broadcast TV is what is illegal. It doesn't need to impact more than one person.

That's not illegal, also this was in the U.K. Governments regulate the airwaves, that authority ends at the antenna. As the original poster already stated in a separate comment, he never transmitted anything that would have meaningfully broadcasted any interference on a licensed frequency band. This is no different than cable, especially considering back in the day cable networks were created to distribute broadcast channels from big antennas at their head end.

This was after weeks of problems and disturbed sleep for a family of 4 and multiple neighbours. And she eventually got a written warning from the local council noise control officer. The immediate thing that follows that is an antisocial behaviour order, usually applied to violent teenagers and the like.

Being respectful of your neighbours is a little understood concept for some people and age and/or disability doesn't exclude your social responsibility to others.