I don't know where they are, but out here in rural Suffolk I can hear gently warbling carriers all over the 430-440 MHz band. They are coming in off the aerial (removing it removes them) but are clearly not amateur. They aren't as rough and unstable as SMPS noise, but as to what they are...
Some time when I'm bored, I'll go out and DF them.
PLT should never have been invented! Stick it in coax and send it underground, I say.