By Margaret Ryan
Thousands of passengers were caught up in airport chaos in August 2006
The discovery of a plot three years ago to blow up transatlantic airliners with liquid bombs disguised as innocuous soft drinks sparked a shake-up of airport security the like of which had never been seen before.
Three men have now been convicted of plotting to kill thousands of people by blowing up planes flying from London to America.
The chaotic scenes of passengers queuing to get through heightened security checks which followed the men's arrests in August 2006 have abated but restrictions remain in place on what liquids can be carried on board planes.
Trials are under way of sophisticated scanners which can identify liquids - but will this mean airline passengers will soon no longer have to pack essential items in 100ml bottles in clear plastic bags or face having them confiscated at security?
UK firm Kromek is developing a scanner which uses an X-ray beam to distinguish between harmless liquids, such as water, and potential explosives such as hydrogen peroxide.
It displays the results as a colour image, allowing operators to ascertain what a liquid is made of, rather than just seeing it is there.
Restrictions on liquids
No liquid in containers larger than 100ml - excluding essential medicines
"Liquid" includes drinks, syrups, creams, mascara, gels and pastes
All items should go in a clear 20cm square plastic bag
Arnab Basu, Kromek's managing director, said the device worked on the same principle as human vision.
"Our brains relate colour to material, otherwise you would have real difficulty in a supermarket if you only saw stuff in black and white."
A trial of the scanner is due to begin in the next couple of months at Manchester Airport, according to a spokesman for the airport.
It is likely to involve a couple of machines at one of the three terminals, he added.
"All the indications are that liquid restrictions are unlikely to be relaxed. So there has to be investment in technology," he said.
A Department for Transport spokeswoman confirmed trials of liquid scanning machines were taking place at various European locations and the UK had significant involvement in technical aspects of this.
"The timing of any easing in the current restrictions will depend on the results of these trials, but in the meantime the present restrictions must remain in place in order to address the real and serious threat from liquid explosives".
She said protecting the travelling public was their highest priority and they would not do anything that put passengers at risk.
Aviation analyst Chris Yates advises companies developing technologies to improve airport security, including Kromek.
He does not believe the end of the bomb plot trial or technological developments will mean restrictions on what can be carried on board planes will be lifted anytime soon.
"This verdict changes nothing. We are still precisely where we were in August 2006," he said.
Mr Yates said while technology can determine what is inside bottles, there are regulatory hurdles to get over before this can be widely adopted at airports.
But he remains convinced the restrictions need to be lifted as soon as possible.
"It causes all manner of backlogs in airport terminals. Despite education programmes by the government and airports that have been put in place, quite a high percentage of people come with too many liquid items."
Certainly airports have had to employ more security staff to deal with the restrictions and continue to confiscate thousands of bottles of perfume, toiletries and drinks.
At Newcastle Airport about 450 litres of prohibited liquids are confiscated every day, with items ranging from vintage Champagne to jars of Marmite.
A spokeswoman for BAA, the UK's largest airports operator, said since August 2006 it had spent tens of millions of pounds on replacing security screening equipment, and had employed 3,000 new security officers across the group.
At Heathrow alone it has employed 1,600 extra security officers which it said had reduced queuing times and had improved passenger security.
Virgin Atlantic said it supported the current security measures saying many passengers had got used to them.
It said it was not currently involved in scanner trials but a spokeswoman added: "With better technology in the pipeline, it's important to keep global security measures under review on an ongoing basis."
For now it seems forgetful or disorganised passengers may still have to ditch their water bottles at the last minute at security as most airport X-ray machines cannot differentiate between a shower gel and a potentially threatening ingredient.
Scanners might pave the way for easing the restrictions on liquids and so inconvenience travellers less, but they would not offer a solution to airport security, according to Philip Baum, editor of Aviation Security International.
"The liquid restrictions should never have been put in place in the first place.
"Governments tend to react to the last plot not the next one," he said.
He believes the emphasis should switch to criminal intent rather than what is in passenger bags.
He said the potential for liquids to be used as explosives was known before 2006 as is the risk of chemical or biological attack.
He wants more effort to be put into profiling rather than the "next bit of kit".
Mr Baum thinks there should be improved risk assessment of passengers and cargo and better background checks on airport staff. He also thinks airport security staff needs to be better trained.
"In terms of terrorism we are up against an extremely intelligent opponent. We need an intelligent response."