Al-Qa'ida's obsession with aviation, it would appear, continues. The foiled cargo plane bomb plot demonstrates that, nine years after the devastating assault on the Twin Towers, the organisation is still intent on using airliners as the delivery mechanism for its terror attacks.

We do not yet know the full story. The Prime Minister, David Cameron, has suggested that the explosive devices – which were concealed in printer cartridges – were intended to bring down the planes on which they were found, possibly over the UK. But the fact that the packages were addressed to synagogues in Chicago casts some doubt on that theory. Whatever the truth, the disturbing bottom line is that plastic explosives were smuggled on to planes passing through the UK and bound for America – and that it was only a tip-off from the Saudi Arabian intelligence services that resulted in their discovery.

What this failed attack does illustrate, however, is the threat posed by Yemen, where the bombs were made and sent from. It is clear that al-Qa'ida has spread well beyond the Afghanistan/Pakistan border. The militants now have a base in the Arabian Peninsula and the Horn of Africa. The argument that the presence of Nato forces in Afghanistan is crucial in thwarting terror attacks on Western targets is left looking threadbare. And the idea that military interventions abroad are effective in stemming terror attacks also sounds increasingly implausible – not least because the individual suspected of being behind this attack, Anwar al-Awlaki, was born and educated in the US.

Air freight security clearly needs to be reviewed – something the Home Secretary, Theresa May, indicated yesterday is already taking place. But an over-reaction should be avoided. There will now be pressure for the White House to order an increase in the number of drone attacks on suspected terror targets in Yemen. But such remote-control attacks, which tend to result in heavy civilian casualties, risk increasing support for the militants in the Arabian Peninsula. Instead, Western governments should work with the Yemeni security services to disrupt the terror networks. That will involve strengthening the weak administration in Sanaa and helping Yemen to deal with a disastrous 35 per cent unemployment rate. It means pressure on the wider region, including Yemen's powerful and wealthy neighbour Saudi Arabia, to increase political freedoms and economic opportunities for its population.

It is the repressive nature of these regimes that stokes the discontent on which Islamist radicals feed. This incident shows that co-operation with the Saudi intelligence services is essential. But it would be a strategic mistake for Western governments to fail to push for political reform in the region for fear of compromising security in the short term.

There is another conclusion to be drawn from these events which should not be disregarded in the rush to address security lapses. What this failed attack, the unsuccessful attempt to bring down an airliner over Detroit last Christmas and the botched Times Square car bombing earlier this year, demonstrate is the somewhat surprising amateurism of Islamist terror groups, rather than their competence and reach.

This is not an argument for complacency. The terror threat against Western targets plainly still exists. And like all terror groups, al-Qa'ida only needs to get lucky once for all its failures to appear irrelevant. But the key lesson from the past week is that with effective intelligence work, efficient security measures and a proportionate official response this is a threat that can be contained.