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London (CNN) -- Two former personal assistants to celebrity chef Nigella Lawson and her ex-husband Charles Saatchi splashed out on luxury goods on company credit cards, a court heard Thursday.

The former assistants, Italian sisters Francesca and Elisabetta Grillo, are accused of fraud. They deny embezzling hundreds of thousands of pounds from the couple.

The first witness, Rahul Gajjar, an accountant for Saatchi, told the court in west London that Francesca had 64,336.97 pounds ($104,500) in expenses on her company credit card in June 2012.

Among the expenses were purchases from designer labels Prada, Miu Miu, Louis Vuitton and Chloe as well as hotel bills and plane tickets.

The court heard that Francesca's average monthly expenditures were 48,000 pounds and Elisabetta's were 28,000 pounds, whereas other personal assistants for Saatchi, a well-known art collector, spent 8,000 pounds or less a month.

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Gajjar said he noticed the sisters' credit card balances had changed at the beginning of 2012. Their average monthly expenditures were previously between 10,000 pounds and 20,000 pounds a month, he said.

He was more concerned about Francesca's balance because it was higher, he said -- reaching about 40,000 pounds "on a regular basis."

The prosecutor asked why he did not raise the matter with Saatchi and Lawson immediately, but Gajjar said he put it "on the back burner" because other matters were more pressing.

"We were dealing with more corporate matters -- more serious corporate matters -- and Mr. Saatchi and Miss Lawson normally didn't have time for what we thought were trivial matters," Gajjar said.

The sisters were expected to make purchases for the family on the company credit card, he said, as part of their job helping the couple with personal and work-related matters.

He said they had a close relationship with Lawson and Saatchi and regularly accompanied the family on holiday.

After an investigation revealed the sisters' alleged personal spending, Gajjar said he met with them in July 2012 to discuss the situation.

The sisters, who didn't have any housing expenses, initially said they were "happy to start paying back" what they had spent on themselves, he said. However, they then rejected the offer and complained of their treatment, he said.

Saatchi's testimony had been expected to follow that of Gajjar, who has been finance director of the Saatchi Gallery Group, part of the multimillionaire art dealer's Conarco Partnership, since June 2002.

However, it became clear there would not be time for Saatchi to take the stand before proceedings finished for the day. Saatchi is expected to testify Friday.

Drugs use allegations

Isleworth Crown Court heard at a pretrial hearing for the sisters this week that Lawson and Saatchi had a "culture of secrecy" around their marriage.

In the hearing, the defense read an e-mail from Saatchi to Lawson about the allegedly embezzled money, saying the assistants would "get off" because, he wrote, Lawson was using cocaine and marijuana on a daily basis and "allowed the sisters to spend whatever they liked."

Representatives for Lawson declined to comment on the allegations, citing the ongoing court proceedings.

The defense also read a statement from Saatchi saying he learned of Lawson's alleged drug use in June, around the time the couple were photographed in a restaurant having an argument.

In the photos -- which were splashed across the front pages of national newspapers at the time -- Saatchi is seen with his hand around Lawson's throat. Saatchi accepted a police caution for assault, and the couple announced they would divorce soon afterward.

The defense alleged that the e-mails showed both Saatchi and Lawson had attempted a "manipulation of the court" and that the case should be thrown out. The judge ruled the trial would proceed.

The prosecution told the court Wednesday that the two sisters spent some 685,000 pounds ($1.1 million) on company credit cards over the course of four years, according to UK media reports. The pretrial hearing had heard allegations the two sisters had spent a lesser amount, about 300,000 pounds, on luxuries.

On Wednesday, Lawson tweeted out a recipe, saying it was in thanks for her supporters.

"Holiday Hotcake: the perfect recipe to show thanks for all your support & to those who hashtag #teamNigella," she wrote.

Lawson, whose culinary skills have long entranced UK audiences, has also appeared as a judge on ABC show "The Taste" in the United States. A second season of the show is due to air in January.

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CNN's Atika Shubert contributed to this report.