Nigella Lawson took cocaine to help her work through the night when she was writing her cookery books, a court was told yesterday.
Lawson found it easier to work at night but "needed help" to stay awake, it was claimed.
But the class A drug caused a change in her personality, leaving her "absent and grumpy", according to her former housekeeper Francesca Grillo.
Grillo and her sister Elisabetta are on trial at Isleworth Crown Court in London accused of fraudulently spending £685,000 ($1.35 million) on corporate credit cards issued by the television cook's former husband, Charles Saatchi. They deny the charges, saying Lawson authorised their spending.
Lawson told the court during her own evidence that she used cocaine only once during the 10 years she was married to Saatchi, but Grillo claimed it was much more often.
She said: "At the beginning of 2012 there were a few episodes where she came down and she had white powder inside her nostril. A few times I ignored it but other times I told her and she said 'it's just make-up'. It was too white to be make-up.
"When she was writing a new book she said she needed to work through the night because she found it easier and she needed help to stay up all night.
"She had a runny nose for a long period of time, and at a strange time, in the summer."
Asked what effect the drugs had on Lawson, she said: "She was going from being very kind and nice to being a bit absent and grumpy in the last few years ... she could be moody."
Grillo also claimed that when she had trouble sleeping, Lawson would come downstairs and smoke cannabis with her children.
She also claimed Lawson's daughter Cosima found a packet containing white powder in a jewellery box in the shape of a hollowed-out book.
Grillo, 35, said that when she saw newspaper pictures of the argument between Lawson and Saatchi in Scott's restaurant in Mayfair in June, she decided the couple must have been arguing about drugs.
"The picture which stuck in my mind was Charles picking her nose. I thought maybe he had the same problem I had, he found some remains inside her nose relating to drugs and I thought maybe if he didn't know that, maybe he didn't know that she authorised all the spending.
"It showed a pattern where she hides the truth and she hides how she actually behaves."
Grillo said she sometimes found rolled banknotes with white powder on them in Lawson's handbags when she was transferring the contents of one into another for her.
She also said Lawson took the Xanax and temazepam, and other medication for depression.