It says
here that "London closed its subway system and evacuated all stations after reports of explosions in at least seven locations on the network." That's aside from the bus explosion.
And
this article reports on at least two explosions at underground stations:
"'We believe there was some sort of explosion. There are some walking wounded at Aldgate,' a police spokesman said, referring to an underground station near Liverpool Street. [..] A London Underground spokesman added that ther has been 'another incident at Edgware Road', north west London. Several people have been wounded at Edgware Road, officials and rescue workers said. Witnesses on Sky television are quoted as saying people streamed out of some of the stations covered in soot, some in tears."
But it also says "Police said power surges are behind the multiple explosion"? The other article also says, "The British Broadcasting Corp. said a power surge may have affected underground trains."