The three bombers who had planned to blow up transatlantic airliners: (From top) Abdulla Ahmed Ali, Assad Sarwar and Tanvir Hussain. (AP)

London, Sept. 7: After two trials and the largest counterterrorist investigation in Britain’s history, three men were found guilty in a London court today of a plot to bomb at least seven trans-Atlantic airliners on a single day with liquid explosives smuggled aboard in soft-drink bottles and detonated by devices powered with batteries.

The convictions came three years after the airline industry was thrown into chaos by the plot. The bombers’ plan to drain plastic soft-drink bottles with syringes and refill them with hydrogen peroxide, a bleaching agent also used as a propellant for rockets, led to new measures prohibiting passengers from carrying all but small quantities of liquids and creams onto flights.

With those measures still in force and causing back-ups at airport security around the world, police and intelligence agencies in Britain and the US had awaited anxiously for verdicts in the six-month trial at Woolwich Crown court in London, where eight men were accused of conspiracy to stage the airliner bombings.

Prosecutors said that plot could have killed at least 1,500 people aboard the targeted planes, which by that measure would have made it second only to the September 11 attacks as the most serious terrorist plot in modern history.

Especially after lengthy trial last year had failed to reach verdicts on the airliner-bombing charges laid against the defendants, the stakes in the second trial for the main agencies involved in uncovering the London plot — including Scotland Yard, Britain’s secret intelligence agencies MI5 and MI6, as well as the CIA, the National Security Agency and the FBI, among American agencies involved — were high.

The political significance was all the greater for the fact that there have been no trials yet for any of those involved directly in the September 11 attacks.

After arrests in the London plot were made in August 2006, documents found on the plotters and on a computer memory stick belonging to one of the plotters showed that they had earmarked airline schedules for seven flights leaving London in the mid-to-late summer of that year for New York, Washington, Chicago, San Francisco, Montreal and Toronto, with aircraft operated by American Airlines, United Airlines and Air Canada.

The idea, intelligence officials said, was to show the world that the security measures adopted after the September 11 attacks were insufficient to foil the kind of low-technology, “asymmetric” attacks favoured by Islamic extremists in their war with the West.

Evidence at the London trial showed that several of the plotters, like those on September 11, had travelled from their homes in the London area to Pakistan and Afghanistan for indoctrination and training by extremist groups linked to al Qaida.

The three found guilty by a jury of conspiring to kill passengers and crew members aboard the flights were the man named by prosecutors as the plot’s ringleader, Abdulla Ahmed Ali, aged 28; Tanvir Hussain, 28; and Assad Sarwar, 29, who was identified at the trial as the “quartermaster” of the plot, responsible for acquiring the explosives, detonators and other equipment that was stored assembled at a “bomb factory” in Walthamstow, a suburb of northeastern London.

A total of eight men were in the dock during the six-month trial.