Italian sisters, Francesca, 34, and Elisabetta 'Lisa' Grillo, 32, are claimed to have "misappropriated" the money to splurge on luxuries such as a £3616 Virgin Atlantic flight to New York and designer goods from Prada, Miu Miu and Chanel.
They were first employed by Ms Lawson when she was married to her first husband John Diamond, who died of cancer aged 47 in 2001.
When she married Saatchi in September 2003, both took roles working for Ms Lawson and her new husband. Francesca Grillo was paid £28,000 a year while Elisabetta was paid £25,000.
Their jobs ranged from looking after Nigella's children from her first marriage - Bruno, now 17, and daughter Cosima, now 19 - and Saatchi's daughter Phoebe, 18, by second wife Kay Hartenstein. They also carried out activities directly related to Saatchi's business activities.
They were sacked last year over the allegations and Saatchi started High Court proceedings against them. They also face criminal charges and are due to appear at Isleworth Crown Court later this year.
Nigella treated them as trusted confidantes, paying tribute to their work in her 2011 cookery book Recipes From The Heart Of The Home by writing: "I give heartfelt thanks to my kitchen confidantes: Lisa and Francesca Grillo."
As a result, the impending cases, according to a source, have created a deep rift between the celebrity chef and her husband.
"The Grillo girls had been very close to Nigella for a long time," the source says.
"She brought them into the marriage and she has naturally been very defensive about all this. I don't think she particularly wanted them to be sued. That's one of the things they were rowing about over the now infamous lunch.
"Charles was criticising her for allowing the assistants free rein and things clearly got a bit heated. One of them was allegedly spending money on Chanel handbags and other designer stuff. He thinks Nigella has been too easy on them."
According to court documents lodged at the High Court of Justice, the sisters' responsibilities included acquiring goods and services for Saatchi, Nigella and their children.
They were given access to two credit cards but only for business purposes. They were also permitted to use a taxi fare account with ComCab, but only 'for journeys undertaken in the course of carrying out their duties'.
But in July 2012, Rahul Gajjar, finance director of the Saatchi Gallery group, claimed that unauthorised purchases may have been made using the credit cards, including a £3,616 Virgin Atlantic flight to New York. Francesca is accused in the High Court document of 'misappropriating' some £166,132 and Elisabetta £5,617.
The pair, were said to be "in flagrant breach of their contractual and/or fiduciary duties as employees".
The writ says Saatchi is expecting to recover more than £25,000.
Another source connected to Saatchi says: "The sisters were often asked to fly to, say Munich, to collect a picture and Saatchi issued the pair a credit card to cover expenses.
"The pair are devout Catholics with previous good conduct with not a blemish on their record.
"It was Lisa who first started working for Nigella as a personal assistant. The story, as I understand it, is that she actually worked for Nigella when her first husband John Diamond was alive - so for longer than ten years."
Nigella is said to have been very upset about the way things ended with the sisters, who have strongly denied the allegations. When approached last week, a visibly upset Lisa said: "I don't want to talk about it."
Meanwhile, Ms Lawson is still living in a Mayfair bolthole after being forced to remove her belongings from the family home. Saatchi is said to be convinced that Nigella's friends have been briefing against him and worried that "lots of dirty linen", could be aired in public in the criminal case against the sisters.
But friends say Ms Lawson is - despite everything - still in love with her husband and after he accepted a police caution for the strangling incident she told the police he had never hit her before.
She is said to be distraught that Saatchi has made no attempt to get in contact with her and friends are worried about her mental state.
"She's been desperate to repair the relationship and desperate to talk to Charles," says one confidante.
"Her plans for the future are to throw herself into her career and America. But she would still consider rebuilding if he would make a gesture.
"She is doing anything she can to get some sort of reaction from him. It is Charles, by his lack of action, who is ending the marriage.
"He is still controlling Nigella, who now feels that she will be dumped without even a sorry or conversation. He has effectively dumped her by stonewalling her and asked her to move her stuff out of the family house."
Another friend says: "Nigella has been devastated by Charles's complete radio silence and the fact that he has just ignored her.
"She has desperately been waiting for a sign or even a sorry and an indication that they can work this out. But he hasn't. Instead he privately blames her for ruining his life and feels that if they reconcile that he will forever be seen as the wife beater.
"He is very worried about his legacy and so has been quietly licking his wounds."
Yesterday, Richard Cannon of Janes Solicitors, who is acting for the Grillo sisters, issued the following statement. "Our clients will continue to vigorously defend themselves both in the civil proceedings before the High Court and the criminal proceedings before the Crown Court."
- Mail on Sunday
