By Frank Gardner
BBC security correspondent
British counter-terrorism and intelligence officials are now working on the assumption that all three failed bomb attacks in the UK have some connection to al-Qaeda - at the very least in motivation and ideology, if not in organisation.
Recently-intercepted conversations, known as "chatter", had already alerted them that jihadists were hoping to attack Britain, most probably in a place where many people congregate.
Police have taken the burned-out Jeep away for examination
But government officials in Whitehall insist there was no "predictive intelligence" prior to the attacks.
They say they were aware of the general background of threats - that's why the UK was at threat level "severe" - but that if they had had any knowledge that Glasgow Airport or London's West End were going to be specifically targeted then protective measures would have been put in place.
The apparent adoption of multiple car bombs as a weapon would mark a new and grisly milestone for al-Qaeda in the UK, but the idea is far from novel.
A van packed with explosives was used in the first attempt to bring down the World Trade Center in New York in 1993.
A plan to load limousines with gas cylinders and detonate them beneath London buildings was discussed by Dhiren Barot and other al-Qaeda associates in 2004.
And in recent years car bombs have become an almost daily occurrence in the mainly Shia areas of Baghdad.
Certainly, the idea of cramming vehicles with fuel and gas canisters is a tactic that has become quite common in areas of Baghdad, particularly in places like Sadr City.
The dreadful pictures we see are nearly always the aftermath of either a suicide bomber who has gone in with an explosive vest, or of a car packed with explosives or simple gas canisters. The problem is that the latter materials are relatively easy to obtain.
So this does mark a change of tactic here in the UK, partly due to the method of operation and partly due to the apparent recruitment of a small cell of individuals of Middle Eastern - rather than South Asian - origin.
UK investigators have been widening their investigation in two principal directions.
They are trying to find and arrest all those connected to the failed bombings.
And they are calling in every resource, both in the UK and overseas, to establish who, if anyone, masterminded the attacks, and what other atrocities they might have planned.
What the police and the security services will try to establish is how long the bombers have been in this country; whether they were resident or moved here quite some time ago; or whether they came in as a sort of hit team.
In recent years a prime focus for the authorities has been to counter the domestic threat from jihadists who go from the UK to Pakistan for training in terrorist camps, such as some of the 7 July Tube bombers.
But that is not to say the authorities have concentrated purely on the domestic threat.
The police and intelligence agencies are thought to be trying to monitor 30 current plots, 200 suspected terrorist cells and close to 2,000 known suspects.
That is a lot of people and virtually all of those have got some kind of international connection.
Back in 2000 there were arrests in Britain before there were any Western boots on the ground in Iraq and Afghanistan; there were arrests of North Africans in Leicester connected to al-Qaeda.
In a way we have come full circle, but this is the first time that al-Qaeda appears to have gone so far down the route of actually planting car bombs in Britain.
In the short term the biggest priority is the man-hunt - catching anybody else in the active cell involved in this particular plot.
As soon as they think they have got those people - and it is probably a limited number - we can expect the official threat level to be reduced from "critical" to "severe" and some of the extra security measures to be relaxed.
This does not mean that the terror threat to Britain will have evaporated. It is more a case of being unable to sustain such a high level of vigilance and manpower indefinitely.