The BBC has a magnificent in-house catalogue of it's folk music material - thousands of items, all annotated and given a reference number.
Two of those numbers are prefixed with an 'S' - not sure if it actually stands for anything specific (secret maybe?), but both items are Irish; 'St Peter's day Was Dawning' and 'Lord Leitrim'.
I understand that both have to be cleared by 'them upstairs' before they can be played on the air.
Jim Carroll