By Laurie Watson

Explosive experts have issued a stark warning that the terrorists at the heart of yesterday’s foiled terror plot could have been planning to disguise liquid explosives as common, everyday items such as mineral water, fizzy drinks and baby milk.

As security measures were rolled out across UK airports, including specific restrictions on taking liquids on board, speculation was rife that evidence had been uncovered of a plot to smuggle liquid explosive devices in hand luggage on to flights.

With several different kinds of liquid explosives potentially involved in the terror plot, security measures witnessed passengers travelling with infants asked to taste the baby milk they intended to carry on their journey in front of security staff.

Explosives expert Dr Sidney Alford, chairman of the explosives company Alford Technologies, said the explosives were not difficult to obtain or make from raw ingredients and could easily be hidden inside innocent-looking bottles or cans.

It would then be a relatively simple matter for a terrorist to move to the aircraft’s toilet to mix the raw ingredients into an explosive cocktail.

“Most people associate explosives with either solid materials or gases,” said Dr Alford. “You don’t expect an explosive to be liquid. If it’s in a baby’s bottle, or a clearly labelled bottle of gin or whisky, or cough mixture, how many security staff are going to question it?

“It’s right that they’re not allowing liquids to be carried on to planes other than milk for a baby, which the mother has to be prepared to taste.

“I think a good move would be to ban all duty-free alcohol on planes. If I were a baddie then I would be very interested in who loads the trolleys before they go on to the aircraft.

“I might for instance have someone aboard, ideally a steward, who knows that a bottle of gin isn’t a bottle of gin.”

Among the host of possible options for liquid explosives were nitromethane, nitroglycerine and methyl nitrate, which were all readily available in small quantities.

He warned that liquid explosives had now emerged as the single biggest threat to air terror threats as they would not necessarily be picked up by “sniffer” type security scanners if placed in carefully sealed and cleaned containers.

Mike Yardley, a historian of terrorism, echoed Dr Alford’s fear of a new kind of terrorist threat, warning that “thousands” could potentially have been at risk.

“You have several hundred people per aircraft and then there is the question of where they were going to do it, as they landed or would they have targeted major cities?” he said.

“We do know, as far as these liquid explosives are concerned, that the terrorists have been developing these techniques and the purpose of it is to defeat existing security measures.”

Mr Yardley asked, “How can you stop people taking every possible liquid on to an aircraft?”