The initial speculation over the nature of the alleged terrorist plot has focused on the fact that almost all liquids have been banned from hand luggage. Not even baby milk was allowed on board flights departing Britain on Thursday unless an accompanying passenger was prepared to taste it in front of security staff.
The Metropolitan police Deputy Commissioner, Paul Stephenson, told a news conference that police believed the aim of the plot was to smuggle explosives onto aeroplanes in hand luggage and to detonate them in flight.
Bottles of water, contact lens solution and liquid medicine are among the items now barred from hand luggage. The Home Office website added that duty-free liquids would also be removed from passengers boarding flights to the United States.
Terrorism experts suggested that the concentration on hand luggage indicated that the plot involved explosives detonated manually rather than through a remote controlled detonator or timer.
”You could carry an inert liquid that if you mix with another one could become explosive,” said David Hill, a former counter-terrorism expert at the National Crime Squad and a security consultant at Red24. ”You could get the materials to make a bomb from a garden centre. Or it could be something as simple as taking on board paraffin and attempting to start a fire.”
Sources told the BBC that the plot may have centred on smuggling explosives on board in fizzy drinks.
With all objects except pocket wallets, purses and a few other essential items also banned from hand luggage, Hill said police would be looking at other ways explosives could be taken onto flights. ”I suppose the average person would think that they were trying to build a liquid bomb. I would think [the security services] are looking at all the possibilities. It could be something else. You can make plastic explosives look like anything, even a bar of chocolate.”
He said it was possible that Thursday’s airport security measures may have been put in place through fears that not all members of the terrorist cell had been arrested and that accomplices might try to carry out the plan before police could track them down.
”The terrorists will have planned this for some time. They will try to make contingency plans and I think that is what the security services will be trying to guard against,” he added. It was too early to say who would have had the capacity to conceive such an apparently audacious plot, Hill added, though it could be related to current events in the Middle East.
US counter-terrorism officials said the plot targeted American Airlines, Continental and United flights between Britain and the US. The US Homeland Security Department raised its alert level to red — the first time that level has been placed on in-bound flights — and all liquids were being taken from passengers boarding flights.
Police sources suggested that the plan involved bringing down up to 10 transatlantic flights simultaneously. With Boeing 747s capable of carrying more than 400 people, the death toll could easily have exceeded that of 9/11, when nearly 3 000 perished.
Professor Paul Wilkinson of the Centre for the Study of Terrorism and Political Violence at St Andrews University said nothing on this apparent scale had succeeded before.
”This is a very ambitious plot indeed, it is the kind of spectacular, potentially lethal attack which the al-Qaeda network has been particularly interested in carrying out,” he said. ”I would be very surprised if it was found that they were not involved as a movement.
”It is possible, I suppose, that some other movement could have copied the kind of techniques that had been used by the al-Qaeda network, but I think that’s unlikely. I don’t think we should in any way underestimate it, it’s a significant and serious development and the authorities are right to be responding with exceptional measures.”
He said the only close comparison could be with the foiled Bojinka plot to blow up 12 Western airliners simultaneously in Asia in the mid-1990s.
The plot was scuppered when plans were found in the Manila base of terrorist Ramzi Yousef, who also planned the 1993 World Trade Centre bombing.
The former Metropolitan police commissioner, Lord Stevens, said such drastic steps would not have been taken unless there was an ”absolute need”.
”You know there is going to be a fair amount of disruption and chaos and that is balanced against trying to keep things as normal as possible. But they will not have done anything unless there was an absolute need for it.”
Airports and aeroplanes have been a key target for terrorists for decades. British-born Richard Reid tried to detonate a shoebomb on a transatlantic flight from Paris to Miami in late 2001. He was overpowered by passengers and later jailed for life by a US court.
In February 2004, six transatlantic US-bound flights from Britain and France were cancelled as a result of security fears. BA cancelled its Heathrow to Washington flight BA223 after receiving advice from the government.
The same flight was cancelled on January 1 and 2 2004, after the US stepped up its security alert. In February 2003, troops and armoured vehicles were sent to Heathrow amid fears that terrorists were planning an attack. — Â