TV cook Nigella Lawson has been described as a "habitual criminal" in court ahead of her former personal assistants going on trial for fraud.

Italian sisters Francesca and Elisabetta Grillo went on trial yesterday accused of using a company credit card to buy themselves designer handbags and flights while working as personal assistants to Miss Lawson and Charles Saatchi.

But lawyers for the defendants had argued that the case should not go ahead due to the "manipulation of the court process" by the TV cook and the millionaire art dealer, who had a high-profile divorce this year.

After hearing submissions from Anthony Metzer QC, defending Elisabetta Grillo, 41, and Karina Arden, defending Francesca, 35, Judge Robin Johnson ruled the trial should go ahead. They both deny the charges.

Mr Metzer said the case should be dropped as the alleged drug use damaged Miss Lawson's "credibility". He said: "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.

"If Mr Saatchi is telling the truth, then Miss Lawson is a habitual criminal."

The trial continues.