The threat posed by Umar Farouk Abdulmutallab should have been identified Photo: AP

What is the biggest division within the Western world since September 11, 2001? Why are we split over Iraq, Afghanistan, policing, human rights, immigration, community cohesion and a dozen other subjects?

It is, at root, a disagreement about threat. This is what Tony Blair explained so lucidly to the Chilcot Inquiry on Friday. On the one hand are those who think that the attack on the Twin Towers proved that there is a global threat to our way of life. On the other hand is a coalition of people who argue that this threat is absurdly exaggerated, or that it is caused by the West’s own aggression.

The disagreement plays out everywhere. In this newspaper today, John Yates, the head of counter-terrorism at the Metropolitan Police, raises the problem of what is known as “profiling”. How should the authorities check passengers queuing for an aeroplane?

Those who pooh-pooh the threat – or say that it is increased by the police’s concentration on particular groups – want only random searches (or none). They put “fairness” first. Those who believe in the threat want to use methods which most effectively foil it. They take their stand on “common sense”.

Sir Paul Stephenson, who became Commissioner of the Metropolitan Police last year, is interested not in politics, but in policing. Unlike his predecessor, Sir Ian Blair, he does not want policing to be permitted or prevented by negotiations with endless political/community/pressure groups. He sees it as a contract with the public. That is why he has pursued a relentless policy of stop-and-search in relation to carrying knives in London. Knife crime has fallen. He rejects “proportionality” about who is stopped and searched if it means that you don’t find the knives. Knife crime in London is a problem evident in young males, predominantly but not exclusively black. So it would be wasting police time to stop and search pedestrians in Richmond upon Thames on a Saturday afternoon.

The Met now want common sense in relation to potential terrorists. They don’t want a stop-every-Muslim policy: that would be almost as useless as random selection, and offensive, too. What they want is a method which assesses all relevant risks. This falls a bit below what the law calls “reasonable suspicion”: it is more like “reasonable grounds” for further inquiry.

Take the Detroit bomber, Umar Farouk Abdulmutallab (he of the exploding underpants). He transited from Nigeria, paid for his one-way ticket from Amsterdam to the US with cash, and was carrying very little luggage – odd behaviour which should have provoked scrutiny.

The famous example is the Syrian agent Nezar Hindawi. In 1986, he tricked his pregnant Irish girlfriend on to an El Al flight to Israel without him. They would marry there, he promised her. In fact, he had planted a bomb on her, timed to go off in flight. The Israeli authorities at Heathrow asked her some questions. Where would she stay? At the Hilton Hotel. How much money did she have? Only £100. Her visit did not make sense. She was searched. The airliner and its passengers were saved, and Hindawi was sentenced to 45 years’ imprisonment.

Anyone who has travelled to Israel will have noticed that the methods of searching passengers are more rigorous than anywhere else, but they are also, on average, less time-consuming. No “fairness” criteria make them search the classic “little old lady”. Long experience has taught them whom to look for.

Israeli experts in the field make some striking points. One is that the authorities need “the entire picture”. It is not only a matter of looking closely at the person in the airport queue. It is also a matter of knowing where and how he bought his ticket, for instance, and whether he has any record of extremism, practical or ideological. And the authorities need to be backed up. They have to know that an officer who follows his intuition will not be frowned on, and subjected to a version of the Macpherson Inquiry into the death of Stephen Lawrence, which paralysed the police for a decade.

What happens at the airport check-in is only the last line of defence. It needs to connect with earlier lines. And this is where the anti-threat people really get in the way.

Look again at the case of the Detroit bomber. He picked up some of his terrible ideas from the Islamic Society of University College London, of which he was president. But the university bigwigs aerate with indignation at the idea that they should try to police such a society.

Look at Major Nidal Hasan, the US Army psychiatrist who shot 13 people dead at Fort Hood, Texas, last November. Colleagues had been worried earlier by his public defence of suicide bombers, but had not dared to complain in case they were accused of Islamophobia. In both cases, the terrorists were admirers of the

al-Qaeda imam Anwar al Awlaki, now on the run. Major Hasan had a lengthy email correspondence with him.

Now switch to Britain. One leading Muslim networker here is a man called Azad Ali. He was until this month the president of the Civil Service Islamic Society (he works at the Treasury). He is chairman of the Muslim Council of Britain’s membership committee, and on the council of the civil liberties organisation, Liberty. He sits on a Whitehall body advising the Director of Public Prosecutions about counter-terrorism and is treasurer of the Muslim Safety Forum, which has an official role in trying to oversee police dealings with Muslims.

In his blog – written, by coincidence, exactly a year before the Fort Hood massacre – Azad Ali described Imam al Awlaki as “one of my favourite speakers… I really do love him for the sake of Allah”. On another occasion, he blogged in favour of a man who argued that it was a duty under jihad to kill British and American troops in Iraq. This week, Azad Ali lost a libel action against a newspaper which had highlighted his words. His case had an “absence of reality”, said the judge. But still Azad Ali is in the Treasury, in the MCB, on the council of Liberty and giving his views about police behaviour in the Muslim Safety Forum.

True, he has dissociated himself from al Awlaki since the Fort Hood massacre; but the story illustrates how difficult it is for our authorities. At every turn, there are bodies like the MSF, stuffed with people like Azad Ali, telling them that they are wrong, insensitive, over-reacting, and racist. And often excusing people like Azad Ali are civil libertarians, such as Liberty, in a weird alliance with some of the least libertarian people imaginable. An “absence of reality” indeed.

There is a threat. Long before it translates into a deadly act, it begins as a deadly thought. To counter it, we must profile it.