British celebrity chef Nigella Lawson has told a court that she’s taken cocaine in the past but says the idea that she is a “drug addict or habitual user of cocaine is absolutely ridiculous”.

The TV cook says she took cocaine with her late husband John Diamond when he found out he had terminal cancer, and in July 2010 when she was being “subjected to intimate terrorism by (Charles) Saatchi”.

“I have never been a drug addict. I’ve never been a habitual user,” she told Isleworth Crown Court on Wednesday.

“There are two times in my life when I have used cocaine.”

The 53-year-old went on to say the first was when her late husband Diamond found out his cancer was terminal, and she had it with him on six occasions.

“It gave him some escape,” she said.

She said she had responsibility for looking after him and the family and earning a living.

Lawson says she spoke to a doctor at the time.

Speaking about the second time in her life, she said it was when a friend gave the drug to her.

“There was another time I took cocaine. In July 2010 I was having a very very difficult time.

“I felt subjected to intimate terrorism by Mr Saatchi,” she said.

Adding that she felt “isolated and in fear of … just unhappy”.

“A friend of mine offered me some cocaine. I took it,” she said.

Lawson said it “completely spooked” her.

“The idea that I am a drug addict or habitual user of cocaine is absolutely ridiculous,” she said.

Lawson said this was her evidence under oath.

She said Saatchi wanted to get revenge on her after she refused to back him over paparazzi pictures that showed him gripping her by the throat.

“He had said to me if I didn’t get back to him and clear his name he would destroy me,” Lawson, 53, told Isleworth Crown Court in London on Wednesday.

“I have been put on trial here, where I am called to answer, and glad to answer the allegations, and the world’s press, and it comes after a long summer of bullying and abuse.

“I find it’s another chapter in that.”

She faced dozens of photographers and television crews from around the world as she arrived at the west London court.

Her former PAs, Francesca Grillo and her sister Elisabetta, sometimes referred to as Lisa, are accused of committing fraud by using a company credit card for personal gain.

Prosecutors claim the Italian sisters lived the “high life”, spending the money on designer clothes and handbags from Louis Vuitton, Christian Dior and Vivienne Westwood.

The pair are accused of using credit cards loaned to them by the TV cook and her ex-husband Saatchi to spend more than STG685,000 ($A1.2 million) on themselves, the jury heard.

Regarding Lisa, Lawson said: “Lisa had been a stalwart and had helped me through a very difficult time when my first husband died.

“I loved Lisa. My children loved Lisa.

“She came to me at a very difficult time in my life.

“She was a rock. I would have done anything for her.”

Lawson, who referred to her multimillionaire ex-husband as Mr Saatchi when giving evidence, said she once took STG7000 out of her savings to pay for Lisa to have her teeth fixed, giving her “incredible confidence”.

She said Lisa left the job at one point and she continued to pay her for three months so she would not get “too anguished” about finding a new job.

She added: “I didn’t want her to feel that she had to stay with me.”

On Lisa’s return, she was “increasingly bitter”, Lawson said.

“She broke our heart.”