"If I was taking drugs to the extent you say, I wouldn't be standing here today. You know as well as I do that regular cocaine users don't look like this. They are scrawny and unhealthy. I value my health and my children have only me as a family. If you think I am going to sabotage my health and leave my children orphans, you are very wrong."
Lawson became increasingly emotional and told Arden: "If you want to put me on trial, put me on trial, but I cannot think that it's right to have me here as a witness for the Crown and treat me like this."
Arden suggested to Lawson that her drug use was a "dark, guilty secret" in her marriage. She replied: "In respect of the cocaine use when my first husband died, Mr Saatchi knew about it." Saatchi earlier told the court he found out this year.
Lawson had a jewellery box in the shape of a book, in which she kept jewellery inherited from her grandmothers and mother and the wedding rings from her first marriage, to John Diamond, who died in 2001.
Arden suggested she also kept cocaine in the box. Lawson said: "I did not."
She also denied that cannabis dealers turned up at her house to sell her drugs.
Arden asked: "Do you agree that you received a Mother's Day card in 2011 or 2012 with a spliff taped to the card saying, 'To enjoy later'?"
Judge Robin Johnson stepped in and told Arden: "That ends your cross-examination. I'm not having any more. You have exhausted my patience."
He told Lawson not to answer the question.
Arden suggested Lawson had used the case "as a vehicle" to settle scores with Saatchi in front of the press.
She replied: "I didn't want to come to court, I would prefer not to because I had been menaced."
While coverage has revolved around the testimony of Saatchi and Lawson, it is sisters Francesca and Elisabetta Grillo who are on trial. They both deny fraud. The case continues.