The allegations against Katrina Leung, said by prosecutors to have had secret affairs with her FBI bosses, have brought inevitable comparisons with the Dutch dancer accused of working for both the French and German secret services during the First World War. Mata Hari was executed by the French in 1917.

Ms Leung, on the other hand, faces up to ten years in prison. But like Mata Hari, she denies using sex to make a fortune as a double agent. “She did nothing to violate her duty, allegiance and oath to this country,” Janet Levine, her lawyer, said.

The case is the talk of Los Angeles society: Ms Leung’s wealthy friends had known her as a successful bookshop owner and local Republican fundraiser. But it is feared that Ms Leung, 49, a naturalised US citizen who was born in China, may have tainted more than two decades worth of US intelligence on China’s nuclear programme.

It is also thought that Ms Leung may have tipped off Beijing about an alleged attempt to plant bugs on China’s presidential jet while it was being refitted in the US. The Chinese said they discovered 27 devices on the Boeing 767 when it was returned, including microphones in the headboard of former President Jiang Zemin’s bed. The US has never admitted such a plot.

Prosecutors say that Ms Leung was having secret affairs with two senior FBI counter-intelligence agents: James Smith and William Cleveland. The former, who retired in 2000, has been charged with gross negligence. Mr Cleveland, who retired in 1993, has resigned from a position at California’s Lawrence Livermore National Laboratory, which develops nuclear weapons and holds highly sensitive secrets. The laboratory said: “While the employee in question has not been charged with any wrongdoing, due to the seriousness of the situation a thorough review of his work is under way.” The authorities have not ruled out further charges.

Prosecutors say that Ms Leung would look in her lovers’ briefcases and secretly photocopy any interesting documents. The items she allegedly obtained from Mr Smith included lists of FBI agents’ names, a memorandum about Chinese fugitives, and information concerning an investigation into Peter Lee, a former employee at the defence contractor TRW. There is no evidence so far that she received any classified material from Mr Cleveland, although the investigation is continuing.

Court papers allege that both Mr Smith and Mr Cleveland had suspected that Ms Leung was a double agent as long ago as 1991. Mr Cleveland is said to have become suspicious when he recognised her voice on a tape, discussing US defence with a Chinese contact known as “Mao”. Mr Cleveland immediately called Mr Smith, who was Ms Leung’s “handler”. It is not known whether the men knew about each other’s affairs. Neither decided to take the issue any further.

The case is yet another embarrassment to the FBI, after its failure to prevent the September 11 attacks; the Robert Hanssen spy case (in which Hanssen was found guilty of selling secrets to Moscow in exchange for diamonds and cash); and the botched spying accusations against a former scientist at the Los Alamos National Laboratory, most of which had to be dropped.

Robert Mueller, the new FBI director, is determined to press ahead with the potentially damaging trial to prove that the agency can police itself.

It is claimed that both Ms Leung’s relationships with Mr Smith and Mr Cleveland continued, Mr Smith having invited her to his retirement party, allowing her to videotape it even though several FBI and CIA officers were present.

Ms Leung — FBI codename, “Parlour Maid” — was denied bail this week ahead of her trial, which is likely to strain diplomatic relations between the US and China. The magistrate said that Ms Leung’s wealth — she has several million dollars spread between 16 bank accounts and property investments — meant she could easily escape to China and take classified documents with her. Arguing against bail being granted, the prosecution said the lack of an extradition treaty with China meant that were Ms Leung to flee, nothing could be done.

Ms Leung’s lawyer countered that in China she would probably face a lifetime in jail for her work for the FBI — or, just as likely, execution. “She’s a loyal American,” Ms Levine said. “Her allegiance is to this country.” Her mansion in Los Angeles had concealed microphones and video cameras to let US agents spy on her Chinese house guests, it was said.

It is also claimed that Ms Leung told interrogators that Beijing had paid her £65,000 simply because Yang Shangkun, the man who gave the order for the Tiananmen Square pro-democracy protest to be crushed, fancied her.

Ms Leung will be arraigned in court on May 12.

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