One of the pioneers of serious coffee in London, and still among the best. The Borough Market branch has a small room at the back where you can sit with an excellent espresso and watch the market trade outside. The roastery in Monmouth Street, Covent Garden, is the original. Simple, honest, no fuss. A good flat white is worth seeking out.
2 Park Street, Borough Market SE1 9AB. Also at 27 Monmouth Street, Covent Garden.