As per title, I have a spare for this. Front stalls, which are now sold out. Selling for face value, which is £15. I can meet in C. London (Russ Square area) any evening this week or Saturday afternoon.
Note: I bought it as a student concession, hence the low price. If you're not a student, or otherwise eligible for a concession, it probably won't be much good to you! If you are, however, then it's a pretty damn good deal for a seat that would otherwise be £30 or so before booking fees.