Charles Saatchi accused his former wife Nigella Lawson of being 'so off your heads on drugs' that she allowed their personal assistants to spend whatever they liked, a court heard.
Italian sisters Francesca and Elisabetta Grillo are accused of using company credit cards to spend £300,000 on luxuries including designer clothes and first-class air travel.
During a 'bad character' application, lawyers for the sisters said they had a 'tacit understanding' that they could keep spending, as long as they didn't 'shop' Miss Lawson to Mr Saatchi for taking cocaine, cannabis and prescription drugs.
Today Judge Robin Johnson read out an email sent from Saatchi to his former wife at Isleworth Crown Court in west London.
In the email, Saatchi accused Nigella and her daughter Cosima, 19, known as Mimi, of taking drugs.
The judge said the email could be reported, despite the trial not having yet started.
Francesca, 34, and Elisabetta, 41, are charged with fraud against Charles Saatchi's company Conraco Partnership.
During a hearing on November 15 Anthony Metzer, representing Elisabetta Grillo, said: 'The bad character application relates to Miss Lawson alleged taking of Class A and Class B drugs and her unauthorised use of prescription drugs.
'This is a matter highly relative to the defence because, in a nut shell, we respectfully submit she had a guilty secret from her husband. She 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.
'It would not have been verbalised, but it would be along the lines of "you do this for me I do that for you".
He added: 'It was not the money being spent, Ms Lawson has her own money, she was independently wealthy, but what the money was being spent on. Her husband would not have condoned such use.
'They had a tacit understanding that they would not shop her to her husband or the authorities.
He added: 'When it all comes to a head through the companies accountant's investigation (into their spending), Ms Lawson is backed into a corner and has to say she did not condone this expenditure.
'She knows that this would lead inexorably to a disclosure to her husband and the authorities about her drug use, which explains why she is saying she didn't consent which is clearly the most important evidence in this case.
The judge at first banned the allegations of drug abuse from coming out as part of the sisters' defence but today lifted the reporting restrictions.