The claims emerged as a judge said that the trial of Italian sisters Francesca and Elisabetta Grillo, who are accused of fraud while working for the now-divorced celebrity couple, could go ahead.
Lawyers for the sisters had argued that the case at Isleworth Crown Court in west London should be dropped because Lawson's alleged drug use damaged her credibility as a witness.
"The defendants' case is that Nigella Lawson lied to her ex-husband about her drug use and about the expenditure that was incurred by the defendants, both expressly and implicitly, because she was fearful of Mr Saatchi's reaction if he knew about the extent of the expenditure and drug use," said Anthony Metzer, representing Elisabetta Grillo.
Metzer argued that the Grillo sisters would not receive a fair trial "as there has been a manipulation of the court process by the two main prosecution witnesses in this case".
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"It's a convenient forum for Mr Saatchi and Miss Lawson to rehearse disputed issues between them... In the criminal courts where, of course, the possibility of libel is not possible," he said.
"If Mr Saatchi is telling the truth, then Miss Lawson is a habitual criminal."
But Judge Robin Johnson ruled that the trial should go ahead.
"I consider, with the right rulings and the ability to monitor the process of the court during the process of the trial, a fair trial can be achieved and therefore I have refused this application," he said.
Multimillionaire Saatchi, 70, and Lawson, 53, who has made her own fortune with TV shows in Britain and the United States as well as a string of cookbooks, split after 10 years of marriage earlier this year.
They announced their divorce after shocking pictures appeared in the British newspapers of Saatchi grabbing Lawson by the neck outside a London restaurant.