Well, to answer my own question: maybe.
I asked at the bag-drop desk and was told by the friendly lady "No, sorry". Deciding to try anyway, we trekked over to the lounge - I have my Priority Pass as a last resort. I gave the lounge angel our tickets, showed my bmi *G, she wrote down our details, and then we found ourselves some seats.
I still don't know if I'm supposed to be able to guest someone in or not though.
The Wilmslow lounge was quite impressive too
, is it really a Servisair lounge?