For information. I found these frequencies being transmitted from the Rothwell NATS site in Lincolnshire when I passed by last week:
NGR: TF 13460 96429
121.325 AM EGPX Scottish ATC SE — North Sea Area ('Humber' sector?) *+
126.925 AM EGPX Scottish Upper (SE) ('Montrose South' sector?) *+
126.783 AMn EGTT London Upper (NE) ("126.785")
125.275 AM Anglia Radar (primary) Southern North Sea (mostly oil rig helicopters)
128.925 AM Anglia Radar (secondary) Southern North Sea (mostly oil rig helicopters)
135.075 AM Swanik MIlitary (NE ICF)
259.6 AM Swanik Military (E ICF) (48FS:6)
270.05 AM Swanik Military (NE secondary)
275.65 AM Swanik Militray (E) (Southern North Sea)
You'll notice I've given up using "Swanwick" as a spelling, and now use the phonetic spelling 'Swanik'.
When compared with 'PrestWick' and 'ShanWick' and 'War(w)ick', our inconsistent language just confuses American pilots
It was a remarkably clueless choice of a name anyway.
*+ I think both of these were offset high, 5kHz or 7.5kHz, although I didn't have sensitive enough equipment to measure by how much.
I found nothing transmitted from the associated mast 3km SSE, so that may just be a receiving mast.