A string of coded e-mails between the terror cell leaders in Britain and their al-Qaeda taskmasters revealed the extent to which the airline plot was being run from Pakistan.

The e-mails were monitored during the investigation and presented in evidence after being obtained from the internet service provider.

Yahoo was served with a court order in California ordering their production.

At the centre of the exchange of messages is a figure referred to as "Paps" or "Papa" - believed to be a pen-name used by a British-born Muslim from Birmingham, who played a key part in recruiting and facilitating al-Qaeda activity in Britain from Pakistan.

The man is reported by US intelligence to have been killed by a Predator drone missile strike on a house in Pakistan's tribal areas last year. But between 2003-06 he was believed to be the key link-man in turning British jihadists who wanted to fight in Afghanistan or Iraq into terrorists and suicide bombers willing to attack their home country.

Abdullah Ahmed Ali, who visited Pakistan several times in that period, was one of the man's protégés. He registered two e-mail addresses while in the Pakistani capital Islamabad in June 2006. For one address he claimed to be an American woman called Tippu Khjan from 'Shepherdstown, West Virginia'. In the second address he used the identity 'Jameel Masood' - again filling in 'United States' under the location heading.

Assad Sarwar, the gang's quartermaster, had similar arrangements for e-mailing contacts in Pakistan - setting up two accounts under false names.

They then allocated nicknames to themselves and the young men they recruited and used codes for the material they were acquiring to make their explosive devices.

Hydrogen peroxide, a key ingredient, was referred to in the e-mails as "aftershave", with price per bottle referring to its concentration. The number of bottles meant the volumes required: with "40 bottles" signifying four litres.

Investigators believed that repeated reference to a rap concert - believed to be a trial run - indicated that the plotters planned to test airport security by sending one of their number on a flight to America in the run-up to the real attacks.

They were also constantly aware of the threat of police surveillance, referred to in the emails as a "skin problem", while "wedding videos" were references to the martyrdom tapes they had recorded.

On 26 June, two days after Ali's return to England from Islamabad, he sent a message to Pakistan saying: "Hi, yeah I'm cool. Got back from holiday. Everything went fine. Didn't get any problems at all. I'm just getting settled, take a few days, then I'll start trading."

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