Celebrity chef Nigella Lawson has ridiculed allegations that she is a regular cocaine user, claiming she would be a lot thinner if this were the case.

Speaking during the fraud trial of former assistants Francesca and Elisabetta Grillo, Lawson said her former husband Charles Saatchi threatened to destroy her when their 10-year marriage fell apart, and attempted to portray her as a drug user to win public sympathy.

The marriage collapsed after Saatchi was pictured apparently throttling Lawson in a London restaurant. Since then he has claimed that she was a regular drug user, even calling her "higella" in a leaked e-mail.

Lawson responded in court: "He told everyone that he was taking cocaine out of my nose at Scott's [restaurant] when he knows that is a lie. People who do that are a lot thinner than I am. I have never been a drug addict."

The cocaine allegations are central to the ongoing fraud case, as the Grillos' claim Lawson allowed them to spend lavishly in return for keeping silent about her alleged drug use.

Lawson also said that she wished to withdraw from the court case, explaining that Saatchi had been "savaging" her reputation and had used a PR blog to turn public opinion against her.

She claimed: "He [Saatchi] said to me that if I didn't go back to him and clear his name he would destroy me and also started spreading false allegations of drug use.

"In particular the awful incident in Scott's and I felt his way of getting this out was to use this case.

"I have been put on trial here, where I am bound to answer the allegations in the world's press and it comes after a long summer of bullying and abuse and I find it [the trial] just like another chapter in that."

'Culture of secrecy'

Lawson admitted that she had taken cocaine half a dozen times with her first husband, John Diamond, while he was dying of cancer. She added that she had taken it again in July 2010 when she was allegedly terrorised by Saatchi.

"A friend of mine offered me some cocaine and I took it. It completely spooked me," she said.

However Anthony Metzer QC, who is defending the Grillos, maintains that there was a culture of secrecy in the couple's marriage and that Lawson's drug use was frequent.

"The defendants' case is that Ms Lawson lied to her ex-husband about her drug use and the expenditure incurred by the defendants. This was because she was fearful about Mr Saatchi's reaction if he knew about the extent of the drug use. Therefore there was a culture of secrecy in their marriage," Metzer said.

He added that his clients had been drawn into the battle between the couple. However, Lawson maintains that Grillo had been a valued employee who later betrayed the family's trust.

"It's very difficult when you find out that someone you have loved and trusted could behave in that way," Lawson stated.