Do you want to become a martyr, the al Qaeda chief asked...

Dramatic details of how the al Qaeda commander behind some of the world's worst terror plots asked a Londoner to target the capital in a suicide attack are revealed today.

In an exclusive interview with the Evening Standard, Abu Omar tells how Khalid Sheikh Mohammed asked him to mount a "martyrdom" operation in London.

Kuwati-born Mohammed, described by the US as "one of the most infamous terrorists in history", is one of six men facing trial by an American military tribunal over the 9/11 attacks.

The suicide bombing request was made in Mohammed's private office at an al Qaeda safe house in the Pakistani city of Karachi. Omar and fellow Londoner Abdul Makim Khalisadar were staying there after fleeing from the frontline of the Afghan war.

Omar also told how another senior al Qaeda leader, Ramzi Binalshibh, urged him to carry out terrorist operations in Britain after the pair became friends during a month of travelling together across Afghanistan and Pakistan. Binalshibh, a Yemeni, is also facing trial over 9/11 and was allegedly only prevented from being on board one of the four passenger jets after failing to obtain a US visa.

The extraordinary disclosures came during an interview carried out with Omar at a London hotel in which he described how he went to Afghanistan in the wake of 9/11 after converting to Islam and found himself alongside some of the world's most notorious terrorists.

His journey was originally prompted by a desire to improve his knowledge of Islam by living under Taliban rule.

It changed dramatically when he was first taught to fire a machinegun in Kashmir, then armed with grenades and a Kalashnikov in Afghanistan, and finally admitted to an al Qaeda terrorist planning summit organised by Mohammed and Binalshibh in Karachi. Potential plots discussed at this meeting, held at a time when the two al Qaeda leaders had been named as key figures behind 9/11, included a plan to blow up the US embassy in Qatar and to kill King Abdullah of Saudi Arabia.

Omar and Khalisadar were asked to put forward their own idea and Khalisadar suggested mounting a grenade attack on a convoy of VIPs.

Omar's clearest insight into Mohammed's aims came, however, when he was asked to go to his office to discuss carrying out terror attacks on his return to London.

"He called me into his private room and asked me if I would be interested in doing a martyrdom operation," said Omar. "I just laughed and said there was no way that I could do that so he said I could go."

Omar added: "Someone had mentioned that he was number three or four in al Qaeda, but I didn't really know that he was such a major figure.

He didn't get too involved with us personally - he just used to come and go and talk to Binalshibh, who spoke English quite well and was the main person who spoke to us.

"The understanding I had was that the people they wanted to go after were Army officers and other people involved in conflict, rather than innocent civilians, because that might harm the jihad. When we had the meeting in the house to get ideas about who we could kill there were about 15 of us sitting on cushions.

"Mohammed and Binalshibh were there and there was an Egyptian who had a white board and we would go up and put our plans on it. I was with Khalisadar and his idea was to attack a convoy of VIPs. Other people suggested bombing a US embassy in one of the Arab countries and killing the Saudi king." Omar said that while he was staying at the Karachi safe house, during January and February 2002, he was also asked by Binalshibh - who had previously visited London - to carry out terrorist activities in Britain, using computers in the former Easy internet café in Victoria to remain in contact and receive instructions.

"He asked would I carry out operations and I asked what that meant and he said, 'Surveillance and that sort of thing'. He didn't give me any targets and there wasn't anything specific mentioned, but I was told to keep in touch when I got back."

Omar was originally raised as a Christian and drifted into crime and drug dealing, but converted to Islam in 2000. He then decided to experience "true" Islamic culture in Taliban-ruled Afghanistan and, despite the imminent prospect of war following the 9/11 attacks, he entered Pakistan in October 200l.

Contacts in the extremist group Jaishe-Mohammed sent him to a training camp in Kashmir where he was taught to fire a machinegun and use a Kalashnikov, before being sent to Afghanistan and a camp close to the frontline outside Kabul. "I could see planes overhead and bombs exploding in the distance and I was scared because I thought I would get captured," he said. As the Taliban resistance crumbled, Omar was taken to another camp outside the eastern Afghan town of Khost where he met Binalshibh for the first time.

"Everyone had weapons so I was trying to get one and Binalshibh was pointed out to me so I asked him and got a Kalashnikov, some grenades, and an ammunition belt with a few magazines on it.

"It was the first time I'd spoken to him, but after that I got quite close to him. He had a car and it was cold in the mountains so he would let me sleep in it. Then I travelled with him in his car to Kandahar - it took two or three days - and stayed with him there.

"We weren't allow to shine torches or use lights, but I didn't know he was a target - he was fairly quiet, keen to help me and used to talk about London where he said he'd stayed in the past. Later, in Pakistan, a picture of him came on television and it said he was wanted, but he just laughed and even then it was in a different language so I didn't know he was such a major figure. I had lived with him for a month or so and when you know someone well it is difficult to imagine them as something else."

After his stay in Kandahar, Omar returned to Khost - where he met another Londoner, Kazi Rahman, for the second time - before leaving Afghanistan with others fleeing the fighting across the mountains into Pakistan in January 2002.

After staying at two safe houses in Karachi, Omar - who has asked to keep his real name secret because of the risk of reprisals over his revelations - returned to Britain later that year where he turned his back on violent extremism.

As well as his opposition to the 9/11 attacks and atrocities such as the murder of US journalist Daniel Pearl, the 7/7 bombings in London - which he describes as "disgusting" - have reinforced his distaste for the methods advocated by some of his former associates.

He now urges other Muslims to learn from his experience and admits that he is fortunate to have survived without being killed, injured or imprisoned.

"If there is anyone thinking about going down the same road, I would say think twice because I am very lucky to be here and people should know what they could be getting into," he added.

Despite his background, Omar is no longer regarded as a danger to the public. A senior Whitehall source said: "We are aware of this individual. He has been actively monitored and it is assessed that he does not currently pose a threat to national security."