Tony Blair may have disappeared from the British political stage but there are some who would have his name up in lights internationally. Nicolas Sarkozy has proposed him as the European Union’s first permanent president, a job the former prime minister would no doubt feel obliged to take (in Europe’s interests, of course). When Mr Blair addressed a charity dinner in New York last week, his hosts expressed the wish that he could stand for the American presidency. No doubt if Mr Blair could, he would.

However, it was what the former prime minister said that has attracted more attention than his future employment. He told us in that speech that Iran is a prime engine of Islamist extremism, exporting and financing terror on an ever-increasing scale. Mr Blair warned that to ignore Iran’s threat would be to repeat the errors of those who turned a blind eye to the rise of Hitler and Mussolini in the inter-war years.

“Analogies with the past are never properly accurate . . . but, in pure chronology, I sometimes wonder if we’re not in the 1920s or 1930s again,” he said. “There is a tendency . . . to believe they are as they are because we have provoked them and if we left them alone they would leave us alone. I fear this is mistaken. They have no intention of leaving us alone. They have made their choice and leave us with only one - to be forced into retreat or exhibit even greater determination and belief in standing up for our values than they do in standing up for theirs.”

Mr Blair’s text could have been George Santayana’s timeless observation that those who ignore the mistakes of history are condemned to repeat them. Although, as the historian Antony Beevor pointed out, politicians tend to push this kind of analogy too far and learn the wrong lessons. Anthony Eden likened Egypt’s President Nasser to Hitler, while Paul Wolfowitz made the same comparison with Saddam Hussein, who was more of a low-rent Stalin. Mr Blair, in arguing for the Iraq invasion, used the appeasement argument and George Bush compared the 9/11 attacks on America to Pearl Harbor.

Even so, Mr Blair is right to warn us about Iran. The regime does sponsor terrorist groups across the Middle East and is actively conniving in the deaths of British soldiers in Iraq and Afghanistan. Its regime vows to wipe out Israel. Its nuclear programme - benign it says - can scarcely be taken at face value after it tried so hard to conceal it from the world.

It is scarcely an exaggeration to say that Iran’s ambitions pose one of the greatest threats to peace in the Middle East. Mr Blair believes the most important lesson of the past is to confront aggression and to do it slowly, firmly and with an unbending will. Opponents of western democracies must always believe that there is the resolve to use force behind the diplomacy and the sanctions. If they doubt that, the cause is lost and Iran will carry on unimpeded.