But Turki is not what he seems. Behind him lies a murky tale of espionage, terrorism and torture. For, while Turki has many powerful friends among Britain's elite, he is no ordinary diplomat. Turki has now been served with legal papers by lawyers acting for relatives of the victims of 11 September.

They accuse him of funding and supporting Osama bin Laden. The Observer can also reveal that Turki has now admitted for the first time that Saudi interrogators have tortured six British citizens arrested in Saudi Arabia and accused of carrying out a bombing campaign.

The revelations throw a stark light on Turki's appointment late last year as Saudi Arabia's new ambassador to Britain. They also cast doubt on the suitability of Charles's relationship with senior Saudis. A year ago Charles had dinner with bin Laden's brother, Bakr bin Laden, and regularly hosted meetings for Turki's predecessor, Dr Ghazi Algosaibi, who was recalled after writing poems praising suicide bombers.

The US lawsuit is seeking more than $1 trillion in com pensation from a list of individuals and companies alleged to have supported al- Qaeda. The claimants' head lawyer, Ron Motley, a veteran of successful anti-tobacco suits, has already called it 'the trial of the century'.

Now, after papers were served on Turki several weeks ago, the Saudi ambassador will be at the heart of it. Legal papers in the case obtained by The Observer make it clear that the allegations are serious and lengthy. Many centre around Turki's role as head of the Saudi intelligence agency. He held the post for 25 years before being replaced in 2001 just before the attacks on New York.

Turki admits to meeting bin Laden four or five times in the 1980s, when the Saudi-born terrorist was being supported by the West in Afghanistan. Turki also admits meeting Taliban leader Mullah Omar in 1998. He says he was seeking to extradite bin Laden at the request of the United States.

However, the legal papers tell a different story. Based on sworn testimony from a Taliban intelligence chief called Mullah Kakshar, they allege that Turki had two meetings in 1998 with al-Qaeda. They say that Turki helped seal a deal whereby al-Qaeda would not attack Saudi targets. In return, Saudi Arabia would make no demands for extradition or the closure of bin Laden's network of training camps. Turki also promised financial assistance to Mullah Omar. A few weeks after the meetings, 400 new pick-up vehicles arrived in Kandahar, the papers say.

Kakshar's statement also says that Turki arranged for donations to be made directly to al-Qaeda and bin Laden by a group of wealthy Saudi businessmen. 'Mullah Kakshar's sworn statement implicates Prince Turki as the facilitator of these money transfers in support of the Taliban, al-Qaeda and international terrorism,' the papers said.

Turki's link to one of al-Qaeda's top money- launderers, Mohammed Zouaydi, who lived in Saudi Arabia from 1996 to 2001, is also exposed. Zouaydi acted as the accountant for the Faisal branch of the Saudi royal family that includes Turki. Zouaydi, who is now in jail in Spain, is also accused of being al-Qaeda's top European financier. He distributed more than $1 million to al- Qaeda units, including the Hamburg cell of Mohammed Atta which plotted the World Trade Centre attack.

Finally the lawsuit alleges that Turki was 'instrumental' in setting up a meeting between bin Laden and senior Iraqi intelligence agent Faruq al-Hijazi in December 1998. At that meeting it is alleged that bin Laden agreed to avenge recent American bombings of Iraqi targets and in return Iraq offered him a safe haven and gave him blank Yemeni passports.