I like this Deke,
my initial thoughts if the sink is not 'live' are a TNCS with a differing potential between sink(true earth) and appliances (supplied earth),
bvut that would involve a distance between Tx and supply and
[would be impossible as TNCS = PME! ] or could this possibly be the case?
BTW, Blackburn isnt a million miles from me, I work close by quite often.