Terror in the skies?

Abdullah Ahmed Ali was described as the ringleader

On Monday three members of an Islamist cell - Ahmed Ali Khan, Tanvir Hussain and Assad Sarwar - were found guilty of a conspiracy to murder using home-made liquid bombs.

The plot came to light after the largest ever surveillance operation in Britain and led to sweeping airport restrictions on carrying liquids onto planes.

In the trial, prosecutors said that the men had planned to smuggle the bombs in soft drink bottles onto aircraft flying from London's Heathrow airport to North America and detonate them.

However, though the three men were convicted of conspiracy to murder, the jury was unable to decide whether or not they planned to target planes.

The jury failed to reach a verdict on four other defendants and one man, Mohammed Gulzar, was acquitted on all counts.

Intelligence officers secretly broke into the Walthamstow house

In Terror in the Skies? Panorama reporter and al-Qaeda authority Peter Taylor investigates the bomb plot - who was involved, how it unfolded, and how the intelligence services worked to avert disaster.

Taylor identifies the Birmingham man living in Pakistan whom the intelligence services believe acted as the crucial link between the cell in the UK and al-Qaeda facilitators in Pakistan.

His name is Rashid Rauf.

Taylor concludes that it was the sudden arrest of Rauf in Pakistan, with the encouragement of the CIA who feared he was about to disappear into the wilds of al-Qaeda's new haven in the Tribal Areas, that forced the UK authorities to swoop several days earlier than planned.

Panorama's story of the liquid bomb plot had an unlikely beginning - a murder on a lonely Birmingham street on 24 April 2002.

After returning home from work in the early hours of that morning, 54-year-old fruit and vegetable delivery driver Mohammed Saaed was stabbed to death as he got out of his car.

Fled the country

The motive was never clearly established but West Midlands police believe it was the result of a family dispute.

Detectives believe the main suspect was the dead man's nephew Rashid Rauf.

Peter Taylor uncovered new information in Washington

Two weeks after the incident he fled from the UK to Pakistan.

In the wake of the 7/7 bomb attacks which hit London in 2005, the UK's intelligence services were given more resources to increase surveillance on suspected Islamist extremists.

In 2006 intelligence officers began watching a terrace house in Walthamstow visited by two men already under surveillance - Ahmed Ali Khan, also known as Abdullah Ahmed Ali, and Tanvir Hussain.

Other men also turned up at the house, but the surveillance teams did not know what was going on inside.

Secret camera

To find out, as Panorama reports, a covert entry team known in police-speak as the "creepers" broke in under cover of darkness.

They were equipped with a night vision camera and once inside installed a secret camera in the wall so they could see and hear on a live video link what was happening. An audio probe had already been planted.

Meanwhile other surveillance teams were watching suspects as they went about their business outside the house.

Intelligence sources say Rashid Rauf linked the cell to al-Qaeda

On one occasion Ahmed Ali Khan was seen meeting an unknown man in the middle of a park, just out of eavesdropping range.

Intelligence officers trailed the mystery man as he left the park. He headed to High Wycombe in Buckinghamshire, a town about 30 miles (48km) from Walthamstow, also home to a large Muslim community.

The unidentified man was Assad Sarwar, who it later transpired was the group's principal bomb maker.

As Panorama reports, officers now watched the suspects around the clock and followed them on shopping trips to chemists, garden centres and supermarkets.

Sarwar focussed his efforts on buying hydrogen peroxide - the crucial liquid ingredient for the bombs - whilst other suspects practised using syringes to remove the contents of soft drinks containers and replace them with the deadly hydrogen peroxide mixture.

By the beginning of August 2006, the intelligence services believed that the plot was about to go live but they remained concerned with gathering as much evidence as possible and then, and only then, moving in to make the arrests.

But as Terror in the Skies? reports, the plan was suddenly brought forward as a result of Rashid Rauf's arrest in Pakistan.

Escape from custody

The fear was that once news of his arrest reached the conspirators via the mobile phone bush telegraph, they would destroy the evidence and go to ground.

Assad Sarwar was the principle bomb maker

Scotland Yard for its part denies that its hand was forced, but as Panorama's investigation shows there can be little doubt that it was Rauf's arrest in Pakistan which triggered the arrests in the UK.

Which brings us back to where we came in… with the murder of Rauf's uncle, Mohammed Saeed, in Birmingham in 2002 in which Rauf was the main suspect.

The judge will determine how long Ahmed Ali Khan, Tanvir Hussain and Assad Sarwar will serve when he passes sentence in October.

But, as Terror in the Skies? reports, for Rashid Rauf the story does not end there. In an extraordinary twist of the story Rauf, the man described by one intelligence source as al-Qaeda's "main guy in Pakistan", remains at large, having escaped from custody in Pakistan.

Whilst he was being transferred back to prison from court, his police guards let him stop at a mosque to pray and he simply ran out of the back door.

An internal US intelligence document that Taylor has seen concludes that Rauf at large "remains a threat to Pakistan - and Britain".

Terror in the Skies? BBC One 10:35pm Tueday 9 September.