As the British are learning, on the verge of losing Basra.

Col Anderson said British troops “did the best they could”, but added: “I’m not sure they did as good a job as they did traditionally. This isn’t Northern Ireland. They thought they had a pretty good model but Iraq is a different culture.”

Michael O’Hanlon, of the Brookings Institution, a Washington think tank, added: “Basra is a mess, and the exit strategy attempted there has failed. It is, for the purposes of future Iraq policymaking, an example of what not to do.

“Basra has gone far towards revising the common American image of British soldiers as perhaps the world’s best at counter-insurgency.”

I think that Petraeus has rewritten the book.