A former personal assistant to television cook Nigella Lawson has claimed she frequently found rolled-up banknotes with white powder on them in her handbag.

Francesca Grillo, 35, who along with her sister Elisabetta, 41, is on trial accused of defrauding Ms Lawson and her former husband Charles Saatchi of £685,000, said she never saw Ms Lawson taking drugs but did find evidence of drug use on many occasions.

She said she first saw the rolled-up notes in the kitchen of the food writer's home in Shepherd's Bush, London, after a party and also in a guest bedroom.

One of her jobs as Ms Lawson's aide was to exchange items between her handbags, and she would find rolled-up banknotes in those, she told Isleworth Crown Court, London.

Asked how often she found the banknotes, Ms Grillo said: "Frequently. Every time I went through her handbag there was some notes. It was very frequent."

Asked if she ever raised the issue of drugs, she replied: "No. I didn't think it was my place."

Ms Lawson would tell ­Francesca, "You're good at finding things", and ask her to look for belongings in her handbags, the jury heard.

She told the court Ms Lawson mislaid things "very often", adding: "Keys, her phone, her mustard."

Asked to clarify, she said: "She likes to carry a tube of English mustard. I know it sounds weird, but that's what it is."

The jury was told Ms Lawson would sometimes come downstairs with white powder on her nose and Francesca would point it out to her, but would be told by the cook it was make-up.

Asked by defence counsel Karina Arden if the substance could have been make-up, Ms Grillo replied: "Too white to be make-up."

She also noted that the TV cook often had a runny nose, the court heard.

Ms Grillo also recalled how she improvised an excuse to protect her employer when a child discovered a hollow book containing what the employee thought were drugs.

The defendant told the court: "She (the child) said 'Look what I found in (the) book'. It was a small plastic bag with white powder. I made up something."

Ms Grillo said the clandestine book also contained items of jewellery belonging to Ms Lawson's late husband John Diamond.

She told the court: "I didn't speak to Nigella (about the discovery). "I didn't think it was my place. I felt close to her but I didn't think it was a nice subject."

She said she found cannabis in a child's room in the home, and Ms Lawson would swig from bottles containing liquid medication.

She told the court: "Tazepam, Xanax ... Ms Lawson had medication for depression. She would take it directly from the bottle."

Asked by Ms Arden how frequently she would see Ms Lawson take medication in this way, Francesca said: "Very often. She had one bottle in the kitchen and one bottle in the bedroom."

The witness said Ms Lawson later became "absent and grumpy", and had trouble sleeping.

She told the court she did not originally mention the alleged drug use in her first statement to police, but did so after photographs of Mr Saatchi and Ms Lawson at Scott's restaurant in Mayfair emerged in the press.

She said: "In the photos she appears to be crying. It shocked me because she said she didn't cry very often in public.

"The one that stuck in my mind was the one of him picking her nose. Maybe he found something relating to drugs.

"I maybe thought if he didn't know that, he probably didn't know about the authorisation - the allowance - of the signatures (by Ms Lawson, on personal expenditure)."

Earlier, the court heard that Mr Saatchi told Ms Grillo he would "destroy" her. Francesca said Mr Saatchi had a "personal vendetta" against her and Elisabetta.

She said Mr Saatchi asked to see her at his home in July after his financial director Rahul Gajjar confronted her and Elisabetta with credit card statements.

The court heard Mr Gajjar had asked the sisters to sign a letter the previous day, admitting dishonesty and promising to continue working for Mr Saatchi and Ms Lawson for a reduced salary for an unlimited period of time. The Grillos had not signed the letter, the court heard.

After she took a cab to the house, Francesca said Mr Saatchi told her she was "stupid" and asked her: "Why didn't you listen to Rahul?"

She said she was falsely accused by him of buying a house on the credit card.

Francesca, who is of Italian descent, said Mr Saatchi told her: "Hide anywhere in Italy but I will find you and destroy you."

The trial continues.