Across the world today governments have to face the problem of terrorism, but in two senses. There is the practical challenge of protecting the public and apprehending murderers. And there is the question of whether we should seek out the “root causes” and try to address them politically, or treat terrorism simply as crime. Where two different terrorist threats are concerned, in Northern Ireland and the Middle East, Tony Blair, the UK prime minister, has taken very different courses, making a distinction that is the more dubious the harder you look at it.

Those opposite approaches might be personified by two people who were closely involved in the Ulster conflict. Conor Cruise O’Brien’s remarkable career in politics and journalism, from New York to London and back to Dublin, has made him a bitter enemy of Irish republicanism. He thinks it should never be propitiated and has long argued that the idea of a “political solution” in Ulster is based on a false concept – the language of “problem” and “solution” is not apt to the case. -- and he insists that terrorism should be treated as security problem, and nothing else.