Coin-op self-service wash and dry, plus a wash-and-fold service if you'd rather drop it off. Ask for Tom behind the counter — regulars do.
It's cash only. Tom keeps change behind the counter, and there's a cash machine at the Tesco Express a couple of doors down if you turn up empty-handed — but it's easier to bring coins with you.
147 Central Street, London EC1V 8AP — a short walk from Old Street station, just off King Square Gardens in Clerkenwell / St Luke's.