Further to my report last night I've had a few responses, confirming my
observations, as far afield as Belgium!
I did some tests last night and this morning, adding to those done on
Sunday morning, with a decent Spectrum Analyzer.
A Word doc. with my findings and some plots is here:
I've sent a copy to Chris Cummings (RSGB Intruder watch) and to John
Gould, as the RSGB are having a meeting with the MCA (coastguard) soon and
this has a bearing on our use of 500, as well as maritime use, since the
offending signal from Faroe is audible on 518kHz.