Whoever proves to be responsible for this, this is more grim news.
No doubt the speculations and rationalisations will begin soon - it will be seen by some as payback for the "provocative" knighting of Salman Rushdie, by others as a warning shot to the new administration to get out of Iraq, and so on.
No doubt many will continue to put scare quotes around "terror" and "war on terror", continuing to deny that London is under attack.
From 2001 to 2005, we knew it would happen in London, but we somehow managed to think it wouldn't. When July 2005 came, we had somehow expected it, but somehow refused to believe it would happen here. Since 2005, the fear abaited, but was always there.
Earlier, of course, we enduring a campaign of Irish Republican terror that lasted from the Post Office Tower attack in 1971 to the Aldwych bus bomb of 1996, the fascist David Copeland's nail bombings of Brixton, Soho and Brick Lane in 1999, and the bombing of the Israeli embassy in 1994, so, on one level, we should be used to it. But I guess you never do.