I can't access the BBC website, but as of 7:27 EST, 6 Blasts Rock London, Killing at Least Two
From the Yahoo article:
Police confirmed an explosion destroyed a double-decker bus at Russell Square in central London. Dow Jones Newswires reported that police said there were explosions on two other buses.
. . . .
Police said incidents were reported at the Aldgate station near the Liverpool Street railway terminal, Edgware Road and King's Cross in north London, Old Street in the financial district and Russell Square in central London, near the British Museum.