Francesca (L) and Elisabetta Grillo leave Isleworth Crown Court in west London November 27, 2013. The two former assistants to celebrity chef Nigella Lawson appeared at court on Wednesday charged with fraud.  REUTERS/Toby Melville (BRITAIN - Tags: CRIME LAW ENTERTAINMENT)

Accused: Francesca and Elisabetta Grillo. Photo: Reuters

Two personal assistants of British television chef Nigella Lawson and her art dealer ex-husband Charles Saatchi say they were treated ''worse than Filipino slaves'' despite defrauding the couple of more than £685,000 ($1.2 million), a court has been told.

Italian sisters Francesca and Elisabetta Grillo face fraud charges in a trial that has already featured allegations that so-called ''domestic goddess'' Ms Lawson hid a long-term cocaine and cannabis habit.

Mr Saatchi, 70, arrived at court but there was no time for him to give evidence on Thursday, while his former wife Ms Lawson, 53, is also expected to testify at a later date in the trial at Isleworth Crown Court in west London.

Multimillionaire Saatchi's finance director Rahul Gajjar told the jury that he confronted the Grillo sisters over their alleged use of the celebrity couple's credit cards to spend £685,000 on a luxury lifestyle.

Francesca was spending a monthly average of £48,000, while Elisabetta was spending an average of £28,000, Mr Gajjar said. Mr Saatchi's other assistants were spending a maximum average of £8000 a month.

They bought themselves flights, hotel stays and designer goods by brands including Louis Vuitton and Christian Dior.

When confronted by Mr Gajjar, Francesca, 35, and Elisabetta, 41, were at first apologetic and Mr Saatchi agreed to let them remain in his employment and to keep living rent-free at a flat owned by Ms Lawson, the finance director said.

But when Mr Gajjar wrote to them outlining how they might pay off their debt, they became agitated, he said.

''Lisa was against the proposal and I remember a reference to 'We're being treated worse than Filipino slaves,''' Mr Gajjar said.

Mr Saatchi and Ms Lawson went to the police after they failed to reach an agreement with the two sisters.

The Grillos deny the fraud.

Their lawyers had argued unsuccessfully on Wednesday that the charges should be dropped because allegations about Ms Lawson's alleged drug use that emerged during the proceedings damaged her credibility as a witness.

The court saw documents from Mr Saatchi on Tuesday in which he described Ms Lawson as ''Higella'' and said she was so ''off her head'' on drugs that her assistants were able to go on spending sprees with her credit card.

Anthony Metzer, representing Elisabetta Grillo, had said that if claims by Mr Saatchi about Ms Lawson's drug-taking were true it would make her a ''habitual criminal''.

Mr Saatchi and Ms Lawson split after 10 years of marriage earlier this year.

They announced their divorce after shocking pictures appeared in British newspapers of Mr Saatchi grabbing Ms Lawson by the neck outside a London restaurant.