Mapsource Topo GB - Trig points

Does anyone have any idea of the conventions that Mapsource Topo GB uses
for describing trig points on the map?

e.g. The trig point at Botton Head (Urra Moor, North Yorks Moors) at
NZ 594 016 is labelled as:-

Botton Head S2988 Pri Pil T Courtney, #797

I assume that the S2988 is a serial number of some sort (It's also
inscribed on the plate on the trig point).

'Pri Pil' maybe Primary Pillar(?), but who is T Courtney, and what does
the #797 refer to?

Garnedd Ugain on Crib-y-ddysgl has:-
Garnedd Ugain Pil Pub Bkt Rem K Stevens 06 04, #2628

and Ben Nevis:-
Ben Nevis Pil Pub S1595 G Jones 4 03, #537

Any ideas?

--
Dave McLaughlin
[censored] Sapiens Non Urinat In Ventum

http://dave-mclaughlin.fotopic.net/