LONDON (Reuters) - Two assistants to celebrity chef Nigella Lawson were cleared on Friday of defrauding her and her millionaire ex-husband after a trial that gripped Britain with tales of drug use and marital strife.

Sisters Francesca and Elisabetta Grillo were found not guilty of defrauding Lawson and art dealer Charles Saatchi of 685,000 pounds ($1.12 million), saying there had been an understanding they could spend anything on credit cards if they kept quiet about the chef's drug taking.

The trial had produced sensational accounts of life in the wealthy couple's household before their high-profile divorce earlier this year after Saatchi was photographed grabbing his wife by the neck in a restaurant.

"My clients are naturally relieved at the verdict of the jury," the Grillos' lawyer Richard Cannon said outside court. "This has been a long, hard fight, played out in the gaze of the world's media."

Such was the huge interest in the case in Britain that even Prime Minister David Cameron passed comment, saying he was a massive fan of Lawson whom he described as "very funny and warm". It was an intervention which led to a rebuke from the trial judge.

A well-known TV star and author in Britain and the United States, Lawson told London's Isleworth Crown Court she smoked cannabis occasionally towards the end of her marriage to Saatchi and had taken cocaine several times in her life but not regularly.

The Italian sisters alleged that 53-year-old Lawson used cocaine, cannabis and prescription pills daily for over a decade.

"DOMESTIC GODDESS"

Lawson, nicknamed the "Domestic Goddess" after the title of one of her bestselling books, grabbed newspaper headlines as she denied the claims in court and rebuked Saatchi for dragging their marital woes into public and trying to destroy her reputation.

"I don't have a drug problem, I have a life problem," said Lawson who is set to be a mentor and judge on U.S. TV cooking show "The Taste" on Walt Disney Co's ABC network in 2014.

Neither Elisabetta nor Francesca Grillo were in the packed courtroom to hear of their acquittal. Elisabetta had suffered a panic attack in court on Thursday, stopping breathing temporarily, and collapsed three more times on Friday, once in the courthouse building.

Lawson and Saatchi, 70, ended their 10-year marriage in July, and he accepted a police caution after newspapers published pictures of him with his hands around his ex-wife's neck.

The fraud case exposed the bitter rows between them, the excesses of their wealthy lifestyle, and their treatment of staff.

Their assistants had allegedly treated themselves to lavish purchases on the credit card without the couple noticing.

The court was told by the prosecution that in the four months to June 2012, Francesca Grillo, 35, spent an average of 48,000 pounds a month and 41-year-old Elisabetta 28,000 pounds.

At various times during the four years to which the charges relate, the court heard, the sisters spent lavishly on flights to New York, hotel stays, designer handbags and clothes.

Lawson told the court Elisabetta had been a stalwart aide who had helped her through the death in 2001 of her first husband, journalist John Diamond, from cancer. She said the fraud allegations "broke our heart".