Charles Saatchi has told a court in London he does not know if he believes allegations his ex-wife Nigella Lawson was a habitual drug user.

Speaking at Isleworth Crown Court, the art dealer said he was "utterly bereft" that a private email he sent the celebrity chef referring to her being "off her head" on drugs has been made public.

"If you ask me whether I actually knew whether Nigella ever took drugs, the answer is no," Mr. Saatchi added as he gave evidence as his two former personal assistants are on trial accused of fraud.

Italian sisters Elisabetta and Francesca Grillo allegedly used credit cards loaned to them by the celebrity couple to spend more than stg685,000 on holidays and luxury items.

Questioned about the email by prosecutor Jane Carpenter, Mr. Saatchi said "I'm utterly bereft that this private e-mail to Nigella has come back to haunt us both. That's all I have to say. The stories that the Grillos were parading was that Nigella had a severe cocaine habit that stretched back a very long time for the entirety of our marriage".

"What I was speculating here was that the Grillos would use this as a defence".

Reporter Ian Woods, outside court, said Mr. Saatchi said he had never seen any evidence that Ms. Lawson used drugs but that he had questioned other members of the household about whether the allegations were true.

Mr. Saatchi told the court he was "heartbroken to have lost Nigella" and said "I wish the last year had never happened".

The 70-year-old said it had been Ms. Lawson's idea to give the sisters credit cards and that they did most of the family's personal shopping.

He told the jury that when he saw the amounts being spent he thought the Grillo sisters had been "naughty" and had wanted to put the matter behind them whereas Ms. Lawson wanted to call the police.