In an interview in London, Janet Napolitano said screening procedures have been improved since the attacks eight years ago, adding: “All but four of the attackers would have been picked up.”

But she said: “You can’t thermoseal entry to the US. We have to be ever vigilant.”…

A spokesman said afterwards: “It should be pointed out that the Secretary was talking strictly about the changes in the travel rules since 9/11. Other estimates, when factoring in increased intelligence manpower, suggest the number of hijackers who would have been interrupted would have been even higher, but the point remains: we’ve come a long way since then, but we can never get complacent.”