A personal assistant accused of defrauding Nigella Lawson and Charles Saatchi has told a court that she saw evidence of regular drug use by the celebrity cook.

Elisabetta Grillo, 41, said she found various signs that Nigella was using cocaine, including a packet of white powder found in a toilet in the home she shared with former husband, John Diamond, as well as rolled-up banknotes and credit cards with white powder on them.

Asked if she had ever seen the TV cook taking drugs, Grillo – who is also known as Lisa – said “No”.

But she told Isleworth Crown Court in west London that she was aware that Nigella had taken drugs and, when pressed by barrister Anthony Metzer QC about what type of substances, she said both cocaine and cannabis.

Grillo, who worked for Nigella as an au pair, said she did not confront the 53-year-old about the issue as she did not want to embarrass her.

She said she thought the celebrity cook knew that she knew about her drug-taking, but added: “I did not want to embarrass myself and her.”

Italian-born Grillo, who is accused alongside her sister Francesca of defrauding Nigella and her former husband, said that, when she was living with Nigella in Shepherd’s Bush around a year after she first started working for her and then-husband Diamond, she found a small packet of white powder in the toilet while cleaning.

She told the court: “I was cleaning the house and I noticed a little packet on top of the loo, toilet.

“I opened it because it was kind of a little funny envelope and I saw white powder.”

On other occasions she said she found rolled-up notes – on one occasion a £20 note – with white powder on them.

“Once I noticed a credit card with white, and a CD, like a music CD, with white stuff,” she said.

Grillo also told the court she found similar evidence when Nigella moved in with Saatchi at his home in Eaton Square.

She said that in a drawer in Nigella’s office she found rolled-up banknotes, including American dollars.

Asked by Mr Metzer if there was anything on them, she said: “Yes, again, white stuff.”

The defence barrister asked her how often over the years she had seen signs of drug use, to which she replied: “Regularly.”

Grillo also referred to a box, shaped like a book, in which Nigella has denied stashing drugs.

The celebrity cook last week admitted taking cocaine with Diamond when he found out he had terminal cancer, and on another occasion in July 2010 during her troubled marriage to Saatchi.

But Nigella, who also admitted smoking cannabis in the last year of her marriage to the art gallery owner, said the idea that she was a drug addict or habitual user of cocaine was ‘absolutely ridiculous’ and accused her ex-husband of ‘peddling’ stories about her alleged habit.

Mr Metzer asked Grillo if Nigella’s assertion that she took cocaine with Diamond, but never again until 2010 was true.

“No”, she replied. “Because I know I saw more stuff before that.”

Asked how often she saw evidence of cocaine use, she said: “Like, every three days, something like that. Regularly, not only once, for sure.”