The general said: “In conventional war, defeat and victory is very clear cut and is symbolised by troops marching into another nation’s capital. First of all you have to ask: do we need to defeat it [Islamist militancy] in the sense of a clear cut victory? I would argue that it is unnecessary and would never be achieved.

“But can we contain it to the point that our lives and our children’s lives are led securely? I think we can.”

He also said the real weapon in the war against al-Qaeda was the use of “upstream prevention” as well as “education and democracy”. The problems that gave rise to militant Islamism were unlikely to be solved soon, he added.