A personal assistant accused of defrauding Nigella Lawson and her ex-husband Charles Saatchi has told a jury that he said he would "destroy" her.

Francesca Grillo (35) said the multimillionaire art dealer had a "personal vendetta" against her and sister Elisabetta (41) who are alleged to have committed fraud by spending stg£685,000 on credit cards belonging to the celebrity couple who were divorced earlier this year.

She told Isleworth Crown Court in London that Mr. Saatchi asked to see her at his home in July after his financial director Rahul Gajjar confronted the sisters with credit card statements.

The court heard Mr. Gajjar had asked them 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 and asked for a copy of it while they considered their options, the jury heard. After she took a cab to Mr. Saatchi's house, the younger sister said he told her she was "stupid" and asked her "Why didn't you listen to Rahul?"

She said she was accused by her then-boss of buying a house on the credit card, which she denied. The defendant, of Italian descent, told the court "He was banging on the table...he said I would end up in handcuffs."

She said the situation became "quite scary" as Mr. Saatchi told her "Hide anywhere in Italy but I will find you and destroy you".

"He said he was going to destroy me and hunt me down. That was his words. His voice was shouting and he was banging on the table and accusing me of various things that were not true. The more he got upset, the more I got frightened. You don't cross Charles Saatchi, everyone knows that".

White powder "in her nostril"

Earlier, she told the jury she "frequently" found rolled up bank notes with white powder on them in Ms. Lawson's handbag. She said she never saw the TV cook taking drugs although she did find evidence of drug use on many occasions.

On a few occasions Ms. Lawson would come downstairs with white powder "in her nostril", she told the court.

"I said to her, 'you have something in your nose. She wiped it away and said it was make-up. But it was too white to be make-up" she said.

The aide 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.

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

The defendant said she often found remnants of cannabis in the house, but never raised the issue of drugs because "I didn't think it was my place".

She also talked about the photographs of Mr. Saatchi with his hands on Ms. Lawson's throat outside a London restaurant.

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

"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)."

She told jurors she raised the evidence of drug use "because it would show a pattern, how Nigella hides the truth and how she behaves".

The jury heard that in the last few years Ms. Lawson became "absent and grumpy" and had trouble sleeping. The ex-PA said the TV cook would "swig from bottles containing liquid medication for depression".

The court has heard the siblings bought designer clothes, shoes and luxury holidays on the cards.

The Grillos, of Kensington Gardens Square, Bayswater, west London, deny committing fraud by using a company credit card for personal gain between January 1st 2008 and December 31st of last year. The trial continues.