Scotland Yard have confirmed in the past minute that there has been a litter-bin bomb between Euston and Russell Square  ( at Tavistock Square ) that has destroyed the top deck of a bus - some witnesses say it was on the bus itself. There are further reports of 2 other bombs going off on buses that are emerging from police and union sources.

It's beginning to look like there has been some kind of terrorist attack taking place. The power surge explanation looks like it's falling apart as I write.
Casualty details are sketchy but we will know more in the next hour.
(UPDATE)There has now been an acknowledgement of "some" fatalities coming from Metronet. It seems to me that there has been a bomb on a tube train somewhere in the underground - possibly around Aldgate. The effects of this have cascaded through the system to cause the power surges that have been reported and the collision that seems to have occurred around Kings Cross.