Nigella Lawson allegedly took cocaine and marijuana ''daily'' for a number of years, a court has heard.

Two former assistants to the celebrity chef claim she was using drugs behind the back of her ex-husband, Charles Saatchi, for a decade and bought their silence by allowing them to use his company credit card for personal expenditure.

Sisters Francesca and Elisabetta Grillo were charged with defrauding Charles out of more than £300,000 - which they spent on holidays, designer handbags and other items - in 2012.

The sisters worked for Miss Lawson for more than 10 years and put forward their ''tacit understanding'' with the 53-year-old celebrity chef as part of their evidence in their case, which a judge has ruled can be used in court.

At an earlier hearing, Anthony Metzer QC, representing Elisabetta, told a court in London: ''The bad character application relates to Miss Lawson's alleged use of both class A and class B drugs and also her unauthorised use of prescribed drugs as a matter which is highly relevant to the defence case.

''In a nutshell we submit that she had a guilty secret from her then husband. She did not want him to know of her use of cocaine and that is highly relevant to the defence case.

''The defendants will maintain that they were fully aware of her illicit drug use and she essentially would consent to their expenditure on the understanding that there would be no disclosure to her husband of her usage.''

Art dealer Charles - whom Nigella walked out on in June after pictures of him with his hands around her throat were published in a national newspaper - was upset when he saw Francesca and Elisabetta's claims and sent an angry email to his ex-wife, which was then seen by the police.

Trial judge, Robin Johnson, read out part of the email in court, in which Charles wrote: ''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 Grillo sisters face accusations of committing fraud using company credit cards. The trial continues.