A few months ago, while in conversation with a prominent political ally of Gordon Brown, I asked him what he thought would ultimately be his man’s election slogan; what form of words would best distinguish him from David Cameron. After a few seconds contemplation, he replied: “Something on the lines of ‘a serious man for serious times’, I suppose.”

After the events of the past few days that sentiment seems stunningly appropriate. A political honeymoon came within a whisker of becoming a national wake. Relief at the failure of these plots should not negate the horror of the situation. If anything, we are underestimating what would have happened if the bombs had exploded.

Carnage such as was planned is, alas, common in the Middle East, but extremely rare in Europe. It happened here to an extent during the Troubles but even then the IRA had to balance its desire to advance what it saw as military objectives with the need not to alienate too many of the Roman Catholic population. Neither the IRA, Eta nor the fringe Marxist sects that arose in West Germany and Italy in the 1970s ever had the mindset of Islamist extremists such as al-Qaeda, its sympathisers and imitators.

So the impact would have been catastrophic in a multitude of directions.

‘Items sent as earthquake aid’

Hidden among clothing were goods selected and purchased to support the activities of terrorists, a court was told

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• Pictures: Glasgow airport attack

BACKGROUND

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It would not only have been the slaughter itself, appalling as that would have been, but also the wider shock waves. Whether the tally of dead had been 5, 50 or 500, the impression left on the watching world would have been of a magnitude many times higher. The numbers of tourists to the capital would have collapsed overnight and London’s astonishing revival as a global financial centre would have been retarded. The atrocities of July 7, 2005, were bad enough but the nervous can find means of avoiding public transport in the city centre if they wish and at modest expense and inconvenience. To abandon the streets altogether is inpracticable. Britain would be viewed by outsiders to be a place of unacceptable peril.

And if the attack on Glasgow airport had come off it would have been almost as disastrous. The loss of life and limb would have been gruesome and the effect on outbound travel from Britain severe. The hit would, once more, have been economic as well as human.

This change in the sadistic techniques of terrorism is chilling in its meaning. Car bombs are among the most basic and brutal of methods. There are 28 million automobiles in this country. To acquire the materials that were packed inside those three vehicles in London and Glasgow is terrifyingly straightforward. There is nothing intrinsically suspicious about buying petrol or gas or nails. A careful plotter might take the trouble to buy them in different places with cash, but he could probably shop for them all in the same store with a credit card and not an eyebrow would have been lifted.

Detonation is more complex, as was mercifully proved by the failure of two mobile phones to serve as the triggers in Central London. But if a fanatic is prepared to take his own life in an attack (and is moderately competent, unlike the perpetrators of the Glasgow outrage), then such technical challenges become an irrelevance.

Since the cost of such an outrage to the country is so high – while the price of it to those willing to undertake it is so low – this is a profoundly unequal struggle. It is not possible to regulate cars, petrol, gas or nails to prevent them falling into the wrong hands, so the only weapon that lies in the hands of the authorities is intelligence.

Yet these plots were apparently not only hatched but taken to the very edge of execution without the police or the security services, by their own admission, being aware of them.

Ministers have to assume that, having come so close to causing pandemonium last week, it is in the interests of al-Qaeda and its affiliates to keep on trying. According to the intelligence community’s own estimates there are at least 2,000 people already living in these islands who are sufficiently radicalised to undertake “martyrdom missions”. To unite a couple of those extremists with the wherewithal required to make a car bomb is not difficult, but it does require a degree of coordination either directly or through the internet. This is the weak link in the terror chain where the chance of being caught is significant.

Gordon Brown and Jacqui Smith, the Home Secretary, must, therefore, consider the following course of action.

First, to boost further the budgets of the intelligence agencies by an instant transfer of resources from the contingency reserve which is set aside in the Finance Act every year and then to reassess funding in the comprehensive spending review that has been inherited by Alistair Darling.

Secondly, to legislate to allow the authorities much more power to control travel between Britain and Pakistan, which – as everyone involved in this field knows – is a route that might as well be labelled the terror trail, such is the traffic that passes through it. We used to have rules that prevented British citizens in Northern Ireland from coming to the mainland without permission. Something similar is required to deal with the route to and from Pakistan.

Thirdly, to salvage what is now a totally discredited system of control orders (destroyed courtesy of the judiciary) by suspending whatever sections of the Human Rights Act may be required and derogating from the entirety of the European Convention on Human Rights if that cannot be avoided. A balance always has to be struck between security and liberty, but the age of the car bomber means it has to be assessed again.

This might seem like a draconian agenda. It is. Yet it has to be done because one sizeable car bomb would blow the most massive hole in Britain’s reputation and well as cause slaughter. A serious man for serious times, indeed. Now is the time to see how serious he will be.

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