She is the impeccably connected journalist turned television chef whose gourmet recipes and flirtatious on-screen presence earned her the nickname the "domestic goddess" and generated a fortune estimated at £15m.

But on Tuesday a London court heard that Nigella Lawson had become a daily drug user, taking cocaine as well as class B drugs and prescription medicines over more than a decade.

Her former husband, Charles Saatchi, after hearing about the allegations of her drug use, described her as "Higella" in an angry email, part of which was read out in court.

The allegation that the 53-year-old, with programmes due for broadcast on Channel 4 and ABC in the United States, was keeping a "guilty secret" – drug-taking – from Saatchi was made in Isleworth crown court by lawyers for the Saatchis' two former longstanding assistants.

Italian sisters Francesca and Elisabetta Grillo are contesting fraud charges in which the two are accused of defrauding Saatchi and Lawson of more than £300,000 while working for the celebrity couple.

On Tuesday the trial judge, Robin Johnson, lifted an order preventing publication of claims made in pre-trial proceedings after the explosive email from Saatchi emerged.

The message from Lawson's ex-husband appeared to show he now accepted the Grillos' claim that Lawson had allowed them to spend freely on the understanding they would not tell her husband about her drug use.

The judge read out part of the email, which had been sent in the runup to the trial: "Of course now the Grillos will get off on the basis that you were so off your head on drugs you allowed the sisters to spend whatever they liked … and yes I believe every word they have said."

The court also heard that Saatchi had made a further statement, which was taken on Monday, part of which the judge read out. In this, Saatchi said: "At the time of sending the email I was completely astonished by the alleged scale of the drug use set out in the statements. Nevertheless I did believe the allegations. I have been asked whether it referred to a belief that Nigella permitted the Grillos to spend whatever they liked. On reflection I was simply speculating the sisters would use this material to defend themselves."

The Grillos are accused of "grossly abusing their position of trust" by committing fraud using company credit cards, spending over £300,000 on luxuries including designer clothes and first-class air travel.

Lawson and Saatchi broke up very publicly in the summer, ending their 10-year marriage. That came after a photographer caught the two in a public row at an outside table at Scott's restaurant in Mayfair, in which he was snapped with his hands around her throat.

During Tuesday's hearing, in which the defence sought to have the case dropped because of "abuse of process", Anthony Metzer, representing Elisabetta Grillo, made fresh claims about a row in which Saatchi also appeared to tweak her nose, in photographs splashed across national newspapers. Saatchi accepted a police caution for assault in June.

"It is our submission the row that happened, resulting in Mr Saatchi assaulting Nigella, may well have had something to do with Nigella taking drugs and may well have had something to do with the issue before this court [of whether Lawson had given the Grillos permission to use the credit cards]," Metzer told the court.

The drug claims first emerged in court at a pre-trial hearing on 15 November when Anthony Metzer, representing Elisabetta Grillo, took the unusual step of lodging a "bad character application" in order to place a question mark over Lawson's reliability as a witness for the prosecution.

He told the court the application "relates to Miss Lawson's alleged taking of class A and class B drugs and her unauthorised use of prescription drugs". He added: "This is a matter highly relative to the defence because, in a nutshell, we respectfully submit she had a guilty secret from her husband."

Metzer added that Lawson "did not want him to know about her use, particularly of cocaine. Because the defendants were fully aware of her illicit drug use, she consented to their expenditure on the understanding there would be no disclosure to her husband of her drug usage."

The drug claim was called "totally scurrilous" by the prosecuting counsel, Jane Carpenter QC, who said the Grillos had made the allegation more than a year after submitting their original witness statement in the case after they were arrested. "The defendants were arrested on 2 August [2012] and the supplementary statement was not made until September of this year," Carpenter said at the 15 November hearing. "By this time the defendants had already admitted their responsibility to the allegations – not least in a letter the sisters sent to Miss Lawson and Mr Saatchi," she added.

Reading the letter out in court, she said: "Dear Charles and Nigella, we are at our utmost despair and we are reaching out to you in the sincere hope that somewhere in your hearts you can find a way to forgive us. We truly believe we had a bond like a family, you were like, as you said to us, like our English family. We saw you like a mother and father figure. There is not a worse feeling than that.

"All we want to do is put this right and make amends. We plead with you to find a way in your hearts to stop the fighting that's destroying us. From the bottom of our hearts we extend an olive branch in the hope that you understand that we never meant to hurt you in anyway. Please forgive us and help us to put this right."

Summing up the application, Johnson said: "The defence asserts that Miss Lawson habitually took cocaine and did so on a daily basis – in addition to her abuse of prescription drugs – throughout the defendants' time in the household."

Lawson has been filming a new Channel 4 cooking competition show, The Taste, based on a US format, in which she acts as a judge along with chefs Anthony Bourdain and Ludo Lefebvre. A second series of the US version, featuring the three, is due to air in January. ABC said in a statement that it had no plans to cancel The Taste, in which Lawson features as a judge: "We have already wrapped production on 'The Taste' and it will air as planned beginning January 2nd."

A spokesman for Lawson declined to comment on the drug allegations "as the proceedings are still live".

The hearing continues.