Two personal assistants to Charles Saatchi and his ex-wife Nigella Lawson complained that they were "being treated worse than Filipino slaves", a court has heard.

The statement was made when they were confronted over their alleged spending sprees on the couple's credit cards.

Rahul Gajjar, finance director for Mr Saatchi, told jurors that Elisabetta Grillo, 41, made the claim after he wrote to her and her sister about their alleged use of the couple's credit cards to buy £685,000-worth of luxury goods for themselves.

Mr Gajjar told jurors that at first Elisabetta, referred to in court as Lisa, and co-defendant Francesca, 35, were open and apologetic about their spending spree.

But he said that after he wrote them each a letter outlining how the sisters would pay off their debt which they were expected to sign, they became "agitated".

"Lisa was against the proposal and I remember a reference to 'We're being treated worse than Filipino slaves'," Mr Gajjar, 44, told jurors at Isleworth Crown Court in west London.

Mr Gajjar said Mr Saatchi and Ms Lawson, who divorced earlier this year, agreed the sisters should stay working for them when the alleged offences came to light.

He told jurors that he suggested that they continue on their current salaries with Francesca, who is alleged to have spent the largest amount on herself, £580,000, expected to pay back £1,000 a month, and Elisabetta £250 per month.

They would also be able to live rent-free at a flat owned by Ms Lawson in Battersea, central London, the court heard.

But Mr Gajjar said the defendants reacted angrily to this.

"They were absolutely in disagreement," he said.

"They felt it tied them to the company for the rest of their lives."

The court heard a series of text messages exchanged by Mr Gajjar and Francesca, including one where she complained her membership at private club Soho House had been cancelled.

"If they carry on doing stuff like this, I won't have any choice but to go to court," she wrote.

In another she said: "If one more small thing happens before we meet, they leave me no choice but going legal."

The court heard that both defendants were given credit cards in Saatchi's Conarco Partnership account with Coutts bank to buy items for the household.

Mr Gajjar told jurors he found out about the alleged fraud after noticing that Francesca's average monthly spend on her card was £48,000 while Elisabetta's was £28,000.

In comparison, the other personal assistants employed by Mr Saatchi had a maximum average spend of £8,000 while the average amount Ms Lawson herself spent on her card per month was just £7,000.

Asked by prosecutor Jane Carpenter why he did not go to Mr Saatchi and Ms Lawson with his suspicions straight away, Mr Gajjar said: "It was on the back burner. We were dealing with more corporate matters - more serious corporate matters and Mr Saatchi and Ms Lawson normally didn't have time for what we thought was trivial matters."

While Francesca's credit limit was £25,000 in June 2008, it went up to £50,000 in February 2010, and rose to £100,000 in June 2011.

Jurors heard that Francesca ran up a £64,000 bill in June last year as she went on luxury holidays and bought designer clothes.

Mr Gajjar said the defendant made dozens of payments for personal use, including more than £4,700 on flights to New York, where she spent £1,850 at high-end fashion store Miu Miu and more than £2,000 on hotels.

She also used the card to pay a £1,280 bill at the Ritz hotel in Paris on the same day she bought a Chloe dress for £723.

On June 12 last year she spent £5,385 at Miu Miu London, and £2,650 at designer store Prada.

Mr Gajjar told the court he met the sisters at the Saatchi family home off the King's Road, west London, on 3 July last year to examine their credit card statements.

He said Francesca explained that some of the transactions were for payments on behalf of her employers, some she was not sure of, and others were personal.

"She admitted that they were for her own use, her personal expenditure, which she was slightly apologetic about and vowed to reimburse the company or Charles," Mr Gajjar said.

He told the court he understood the sisters had been employed by "Nigella's team" originally before coming on to the payroll of Conarco Partnership some time between 2006 and 2008.

But he said the defendants' credit card bills would be paid off in full every month from Saatchi's personal account.

Mr Gajjar said he checked the statements, but when asked how thoroughly he did this, he said: "Just the quick once-over really."

Francesca lived with the Saatchi family in their home in Eaton Square, Belgravia, before moving with them to their home off the King's Road, he said.

Asked by Ms Carpenter to describe how the defendants got on with the family, Mr Gajjar said it was a "good, close relationship".

The Grillos, both of Kensington Gardens Square, Bayswater, London, deny the charge against them.

It is alleged that, between January 1 2008 and December 31 2012, they committed fraud by abusing their positions as PAs by using a company credit card for personal gain.

Mr Saatchi is expected to give evidence later today.