A British Muslim described by police as an al-Qaeda mastermind who considered mass murder to be part of his duty became the first person to be convicted of the charge of directing terrorism yesterday.

Rangzieb Ahmed, 33, was part of a three-man cell on an unknown terrorist operation in Dubai and Saudi Arabia in December 2005 that was aborted. He was regarded as so important that a second man, Habib Ahmed, 28, was recruited to carry on his behalf incriminating documents in invisible ink that amounted to a “terrorist’s contacts book”. Among the names and numbers in the three books was that of Hamza Rabia, No 3 in al-Qaeda’s chain of command.

Rangzieb Ahmed, of Rochdale, was convicted at Manchester Crown Court of directing terrorism - an offence introduced by the Terrorism Act 2000 – after an 11-week trial.

Habib Ahmed, a Manchester taxi driver who is unrelated to Rangzieb Ahmed, was found guilty of being an al-Qaeda member but cleared of attending a terrorist training camp in Pakistan in 2006. Mehreen Haji, 28, Habib Ahmed’s wife, was cleared of arranging funding for terrorism.

Senior officers of Greater Manchester Police’s counter-terrorism unit claim that their three-year investigation into the terrorist cell was instrumental in disrupting and destabilising the senior levels of al-Qaeda.

Rangzieb Ahmed travelled to Dubai from Pakistan via China in December 2005 and was due to fly on to South Africa as part of a “major activity”, but the plans went awry when a third man, Hamza Rabia, was blown up.

Counter-terrorism officers from Greater Manchester Police were monitoring the two Ahmeds and bugged their hotel room in Dubai, where they made several coded references to al-Qaeda. The surveillance continued in Manchester.

Rangzieb Ahmed, who admitted belinging to the proscribed Harakat-ul-Mujahideen, flew to Pakistan in January 2006 and was arrested there. This forced the hand of counter-terrorism officers in England, who arrested Habib Ahmed before he could flee.

Two of the invisible-ink diaries were discovered at Habib Ahmed’s home. The third has never been recovered. They appeared to be blank but contained names, phone numbers and e-mail addresses of key al-Qaeda figures.

The two men are due to be sentenced today. Before the trial the judge, Mr Justice Saunders, rejected an application by the defence team that the case should be thrown out because British intelligence services had colluded in Rangzieb’s torture while he was detained in Pakistan. Rangzieb claimed that he was beaten, had three fingernails ripped off with pliers and was incarcarated without trial for 13 months before being flown illegally to England.

He alleged that while he was kept blindfolded, hooded, manacled and shackled his torturers were supplied with questions by MI5, two of whose agents also questioned him.

The judge suggested that the removal of the fingernails dated to Rangzieb’s earlier detention in India.

After the hearing Detective Chief Superintendent Tony Porter, of GMP’s counter-terrorism unit, said: “Rangzieb Ahmed consorts with senior terrorist figures and has devoted his life to creating and working with terrorist networks. We believe he was intent on masterminding terrorist attacks and would have considered mass murder part of his duty.”

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