I found a mention of a fish-finder product somewhere and now I can’t for the life of me find it again. But that must have been a mistake, as this range is reserved for other uses according to OFCOM.
If #2 is a ship-shore thing, the question is "where’s the shore?". Mallaig or Stornoway are the only possibilities I can think of. Stornoway is not particularly close, but then neither is Radio 4. Mallaig seems much more likely because it’s very close, but the power could be anything and easily could override the distance.
One really weird thing that I have noticed is that the spike #1 - Radio 4 - is not seen on line #1, but is seen on line #4. How can that be? It’s quite distinct, quite high, not just marginal so as to easily get buried in the noise; about 5.5dB high above the noise floor. I though to myself "better balance, better common-mode rejection" (if that’s the correct term?), but then spike #2 is seen on the other modems.