Saturday morning at The Kernel is worth doing. You can get the tube to Bermondsey from Southwark or London Bridge. The Euston Tap at Euston Station is an excellent pub, as are any of the Craft Beer Co. ones in Clerkenwell, Islington and Pimlico. Camden Town Brewery's bar at Kentish Town West station is open at weekends, where you can take refuge from all the real ale with some quality lager. BrewDog have a place up in that direction too. For more traditional pubs it's hard to beat The Harp on Chandos Place near Covent Garden, or for the hardcore beards-and-sandals experience (apart from GBBF itself), the Wenlock Arms, near Old Street.