Definately worth a call if you are in the Shoreditch area of London is Present, where Gwilym Davies (2009 World Champ Barista) is serving coffee.
I have had some wonderful coffee (both espresso and cappuccino) at Gwilym's and he's using a lever machine (unusual to see these days), which is fun to watch!
If you are making the journey he is at 140 Shoreditch High Street which is a 10-15 minute walk from Liverpool Street station depending upon your walking speed.