There is a lounge at SSH. Make sure you get an invite at check-in though, or you won't be able to gain access. A couple on front of us were flashing their BA Silver cards, but were refused entry.

The lounge is basically a big open area on the top floor. There is tea, coffee, beer and wine. Along with some pastries and snacks. Great views over the airfield.

Note that you need to arrive quite early if you want a seat. There are relatively few seats, so a full BA777 with NCW and Golds/Silvers fill it up pretty quickly.