@new in '82 - someone on the board flogged me an 18t Surly sprocket, just popped this on the opposite side to the standard 15t as it comes with fixed/fixed hub as standard. Very simple you just need a spare lock-ring. This'll give you 48/18 (about 70 if I remember correctly). I've never ridden fixed before now and it seems like an ideal gear for London.

And finally ;) here it is with the newly trimmed saddle, I'm pleased with it but each to their own: