So now we know. The bombers of London's public transport last Thursday were suicide attackers from Leeds. These young men, of Pakistani origin, appear to have been unknown to the authorities and unexceptionable within their communities. What they must not be is underestimated by society.

For the sake of mass murder they were capable of giving up their own lives. For the victims of this vicious assault and those they left behind the tragedy is much the same, but that the bombers were home-grown makes this, in terms of policy and society's response, an even more chilling challenge than had they come from abroad.