There is no point denying that our closeness to the United States is probably one reason why Britain was chosen. Al-Qaeda would regard the murder of thousands of people flying between the two allies as a propaganda triumph. Across the Muslim world the streets would fill with crowds celebrating the carnage.

More subtly, had the plot succeeded it would have been a massive humiliation for Britain that would have strained US-British relations.

Al-Qaeda may regard Britain as a weak link in the West’s security. In 1988 British airport security was criticised when a suitcase bomb brought down a Pan Am plane over Lockerbie. Our security services identified Mohammad Sidique Khan (one of the London bombers) as a threat but failed to keep tabs on him. When police killed an innocent man, Jean Charles de Menezes, and at Forest Gate shot a man who was then not charged, British intelligence looked amateurish. On this occasion we must congratulate heartily those who have smashed the conspiracy.

As 7/7 demonstrated there is a pool of Britons lurking within our sizeable Muslim community who will joyfully commit suicide and mass murder.

The scale of the aircraft plot suggests that in Britain Al-Qaeda can easily assemble quite large numbers of self-styled martyrs. The men who flew planes into the World Trade Center and the Pentagon were foreigners in the US, mainly Saudis. Al-Qaeda is bound to favour indigenous terrorists who attract less attention. Unfortunately, for years Britain paid little heed to the threat from Islamic extremists. Hundreds of young Britons have been radicalised in mosques at home and trained in terror schools abroad.

Last week, before the bomb plot was public knowledge, Tarique Ghaffur, an assistant commissioner in the Metropolitan police, warned that anti-terror legislation and insensitive policing make British Muslims feel victimised. As far as that statement goes it is a victory for Al-Qaeda. Each terror plot increases the pressure on the Muslim minorities in western countries. It would be illogical and dangerous if our counter-terror efforts did not focus on those communities. But as we intensify those activities we make new enemies within our population. Those tensions offer Al-Qaeda a route to bring down the democracies that represent the antithesis of its world view.

So those who argue that Britain has brought terror to its shores by supporting George W Bush should admit that we have imported it unwittingly by recognising our obligations to Commonwealth countries such as Pakistan, by pursuing liberal policies on immigration, by extending asylum to those who faced “persecution” without much reflection on why they found themselves in that position, and by ignoring the activities of “dissidents” based here, despite warnings about them from allies such as France and Saudi Arabia.

More uncomfortably still for those who argue the simplistic anti-Bush line, Britain could be an Al-Qaeda target precisely because it is a nation divided and given to self-flagellation. After the Lockerbie bombing it fell to me as a transport minister to meet some of the grieving relatives. One man who had lost his daughter told me that he blamed airport security, not the terrorist. Even allowing for his suffering I can make no sense of the remark, but it seems to typify a misplaced magnanimity that springs from unwarranted collective guilt.

Terrorists are alive to our vulnerabilities. In 2004 Al-Qaeda attacked trains in Madrid hours before the Spanish general election. Jose Maria Aznar, ally of Bush and Blair, who had been expected to win, lost. The new government scurried to withdraw Spain’s troops from Iraq. Was Spain targeted because it supported America, or because it could be intimidated? Perhaps the US has been spared attacks at home since September 2001 partly because its security is good, but also partly because terror unites Americans more than it divides them.

In this country discontent with Blair’s foreign policy has reached fever pitch. From a pipsqueak parliamentary private secretary to Jack Straw, the former foreign secretary, Labour politicians vie with each other to wear their conscience on their sleeve and distance themselves from Blair. As Israel fights terror the Tories are mealy mouthed and Gordon Brown is silent.

Might not Al-Qaeda reasonably believe that another massive atrocity could bring Blair’s leadership to an end and usher in a series of less hard-nosed administrations? Might they not also reason that Britain is a tempting target because in vast numbers the British refuse to recognise the nature of the extreme Islamist threat that confronts us?

For many Britons a new massacre would supply fresh evidence of the wickedness of the Iraq war or the plight of Palestinians or the downtrodden condition of British minorities. The more obvious explanation, that a group of religious fanatics is bent on destroying us and achieving world domination, would somehow elude them.

In the United States the Democrats (especially Ted Kennedy) are behaving disgracefully, scoring political points by claiming that the conduct of the Iraq war has made America more vulnerable. That may indeed be true but it is irrelevant.

The assault by Al-Qaeda on Muslim governments and against the West cannot be sidestepped. Pacifism is not an option. It does not inoculate against terror. Al-Qaeda launched 9/11 to open a front between Muslims and the rest. The West’s failures in Iraq may have helped Al-Qaeda to attract more recruits. But if the invasion had not occurred, Saddam Hussein’s untamed defiance would have encouraged Al-Qaeda too. Western weakness would have made the fundamentalists believe that victory was easy.

British commentators mock Bush’s “war on terror”. To me the idea of not waging such a war seems more contemptible and risky. I am more inclined to question Bush’s idealistic plan of combating terror by spreading democracy to Muslim states.

Removing Saddam has allowed Al-Qaeda into Iraq. It is hard to believe that infant democracies in Saudi Arabia, Morocco or Egypt would suppress terror more effectively than their present leaders. Nor is Bush hurrying to replace General Musharraf in Pakistan. Even long-established democracies such as Britain and France are wondering how liberty and the defeat of terror can be compatible.

This is not a good day to wave the flag of civil liberties, and so I will. The day before news of the plane plot broke, John Reid, the home secretary, again addressed the issue of why we need to detain some people without trial or even charge. Once more I was left unconvinced.

Indeed my suspicions were heightened because much of his argument focused on how nasty fundamentalists are (for example, in their treatment of women). That has nothing to do with how it is that he apparently knows that some people are very dangerous, but cannot prove it in a court of law. In the wake of last week’s news parliament will give the government yet more draconian powers if it requests them. Ministers bear the responsibility to act honestly and with a good conscience.

For these are times when we expect our politicians to metamorphose into statesmen. Blair has never disguised his ambition to play Churchill, and truly his oratorical skills are superb. The problem is that while the words still come to him, his audience has drifted away disillusioned.

David Cameron and Gordon Brown must step forward to give Britain leadership. If the political class does not unite we will be in more danger from terror. Unless our leaders educate the British people on the unavoidable threat that we face we will be more vulnerable. Brown and Cameron, even more than Blair, must become statesmen. Let us hope that they can rise to the occasion.

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