“People will judge us on the basis of whether we did everything we could,” she said. “They will not forgive us if we spend our time floundering because it was all too scary.”

Ms Blears said the government would issue further guidance in leaflets and through web sites on what to do if there was an attack.

“You should have all the telephone numbers you need and know what’s going on in your children’s schools,” she said.

“Most people would be sensible about water and making sure they have some tinned food. A lot of it is common sense.”