One of my editors at the BBC grew up in Belfast during the Troubles. I happened to run into her on the day of the second Istanbul bombings. "What does it remind you of?" she asked.
"I know. Exactly," I replied. She didn't mean that those of us who'd lived in Belfast had ever experienced suicide bombings, nor was she making any facile literal comparison between what happened in Northern Ireland and this new war. What my friend meant was that fear of sudden, violent death was a fact in our lives once again.
With Christmas coming we were reduced to a useless routine of risk calculations. Do I get the Tube down to Chelsea? Do I let my son go into the West End with his grandmother? Do I retreat into my little corner of west London until the threat goes away? But it's useless because I don't know when, if ever, the threat will go away. It's also useless because the terrorists have the advantage every step of the way. A few men hiding out in our suburbs have knowledge that can change lives irredeemably. I know nothing. Not the places they may target nor the time of day nor the size of the bomb. Not even the security services know. They have some information but like the rest of us don't know when the hammer will drop.
They are warning that two al-Qa'ida cells are operating in Britain, and with the imagery of Istanbul playing out on our television screens how many families are wondering if London or Manchester or Glasgow will be next? For the fact is that sooner or later the suicide squads will get "lucky" here. As the IRA chillingly warned Mrs Thatcher in the 1980s after Brighton: "We only need to get lucky once. You need to be lucky always." Luck as defined by a suicide bomber is the chance to blow as many people into small pieces as possible. They can be mothers, fathers, sons, daughters, babies or old folk, fit or disabled. They could be someone in Istanbul or Cardiff, or you or me.
The differences between this and the attacks of the Troubles outweigh the similarities. I don't wish to mitigate the horror perpetrated by the IRA and the loyalist paramilitaries but the "kill every living thing" tactics of suicide bombings were unknown in Ulster. There were some horrific exceptions when civilians were deliberately targeted by bombs, and some cynical screw-ups, but the IRA generally tended to telephone warnings.
They were even known to issue apologies for bombings in which civilians were killed. You might treat these with a large grain of salt but such statements did at least reflect a sensitivity to public and political opinion. This grew as Sinn Fein became a major political force, and there was a political agenda around which negotiation was possible. The physical force element in Irish republicanism might have ruled out compromise on the demand for a united Ireland for many years, but it never totally ignored the idea that some compromise settlement with the Protestants of Ulster would be needed. Even at its most atavistic, militant Irish republicanism realised it could not annihilate the opposing tradition. On both the loyalist and nationalist sides the number of true believers in a sectarian fight to the finish was very small.
Not so with al-Qa'ida. In the wake of the 11 September bombing, Michael Ignatieff coined the phrase "apocalyptic nihilism" to describe the agenda of al-Qa'ida. It is a phrase which encapsulates what we think we know: that the suicide bombings have no aim but to inflict pain and confusion. But this is not the entire truth. There is another formulation of Ignatieff's which might help us to understand rather more. When describing the impulse for genocide, the Canadian writer and human rights scholar sees at its root a desire for utopia. In a memorable essay he asks, "What could be better than a world without enemies?" Ignatieff argues that this notion was at the root of Hitler's quest for the perfect German Reich; it propelled the excesses of Bolshevism and Stalinism and later inspired Pol Pot and the genocide of Rwanda.
If the campaign being waged by al-Qa'ida and its allies was directed solely at achieving a political advantage on the Palestinian issue, or the US occupation of Iraq, it might be more easily compared to the conflict in Northern Ireland (ie a campaign fought with ferocity but for goals around which negotiation was sought). But there are no spokesmen for al-Qa'ida who present themselves to the press; there is no point-by-point plan for negotiation and nobody will be standing for election.
When Osama bin Laden speaks it is not as Iran's Ayatollah Khomeini spoke, with a religious and political programme, but as a messiah of the absolute. I have been re-reading bin Laden's statements and interviews and they have lost none of their power to chill. They are also curiously contradictory. Bin Laden will, for example, say that the killing of women and children is forbidden by Islam yet go on to declare that there are no innocent victims.
Yet the primary problem is not of logic but of location. How do the Western powers fight such an enemy when he is everywhere and nowhere? At the time of Iraq war I toured Arab capitals and came away with the impression that the ranks of al-Qa'ida were swelling. This belief was based purely on the numerous conversations I'd had in refugee camps and coffee houses in Amman, Cairo and Beirut. It seemed to me that a profound radicalisation was under way. A diplomat friend was inclined to disagree, telling me that recruitment might go up slightly but it wouldn't surge. I don't know about a surge of actual suicide bomb volunteers, but the ranks of fellow-travellers has definitely risen substantially.
In the wake of 11 September there was much written about the need to get "humint"(human intelligence) on al-Qa'ida. The idea was that men would be recruited from the Islamic community who could infiltrate the terrorist cells. That was wishful thinking. It assumed the existence of a common cause great enough to risk one's life for. But how many young men from the Arab street, men plausible enough to impress as potential al-Qa'ida volunteers, want to line up alongside Western intelligence? The answer is very few.
When you write a column you are expected to have an answer tucked in at the end, the argument tied up neatly. In these frightening times we seek the consolation of a simple solution. But on this war I have no answer. Certainly no simple one. The war will go on. I don't know for how long. I don't know how it will end. I don't know where the bombers will strike next. That is what terrorism achieves. We are cast into a perpetual state of unknowing.
So in acknowledging that I don't know, I will speculate and say that what might work is the patient business of intelligence gathering and politics. If the aim is the incremental weakening of the military structure of al-Qa'ida, a whittling away of the organisation's capacity to attack, alongside - critically - a political programme that tackles injustice in the Middle East, there could be hope of peace within a generation. This much I do know: we are talking possibility here, not probability.
The writer is a BBC Special Correspondent