Charles Saatchi has told a court he was "utterly bereft" that a private email he sent to ex-wife Nigella Lawson referring to her being off her head on drugs has been made public.

The email he wrote to the TV chef was read in full to jurors but, when asked if he believed allegations that Miss Lawson was a habitual cocaine user, the art dealer said: "I do not know."

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

Italian sisters Elisabetta and Francesca Grillo are accused of using credit cards loaned to them by the celebrity couple to spend more than £685,000 on themselves.

Saatchi listened as the email he sent to Lawson on October 10 was read out to jurors at Isleworth Crown Court in west London.

In it he referred to his ex-wife as 'Higella' at one point.

He wrote: "Nigella, I was sent these by a newspaper and I can only laugh at your sorry depravity.

"Of course now the Grillos will get off on the basis that you ... were so off your heads on drugs that you allowed the sisters to spend whatever they liked and yes I believe every word the Grillos have said, who after all only stole money."

The email went on: "But I'm sure it was all great fun and now everything is perfect - bravo, you have become a celebrity hostess on a global TV game show. And you got the Pass you desired, free to heartily enjoy all the drugs you want, forever. Classy."

Questioned about the email by prosecutor Jane Carpenter, Mr Saatchi said: "I'm utterly bereft that this private email 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."

Mr Saatchi said Miss Lawson was "very cross" with him when he told her he had confronted their personal assistants about their alleged misuse of his company credit card.

The multi-millionaire, who went through a high-profile divorce from the food writer earlier this year, said he thought the Grillo sisters had been "naughty" but he wanted to put the matter behind them while Miss Lawson wanted to call the police.

Mr Saatchi said he told the pair that they could pay the money they owed off and live rent-free in a house in Battersea, central London, that Lawson used for filming but his then-wife did not agree.

"She was very cross with me," he told jurors.

"And she said 'How could you do that? I would never have them in my house again...'

"And I said 'I'm really sorry. I was trying to cause the least friction possible and didn't want a lot of disruption...

"'Sorry if I misread it'."

Mr Saatchi went on: "She then said 'You have to hand this matter straight over to the police'."

It is alleged that the Grillo sisters lived the "high life", spending the money on designer clothes and handbags from Louis Vuitton, Christian Dior and Vivienne Westwood.

Referring to the atmosphere in the family home before the breakdown of his marriage to Ms Lawson, Mr Saatchi said: "It was a happy home where everyone just buzzed around happily."

He said he was "utterly heartbroken at having lost Nigella" and said he wished this year had never happened.

When asked if he had adored Ms Lawson during their marriage, he said: "I adore Nigella now. I absolutely adore Nigella and I'm broken-hearted to have lost her."

Mr Saatchi said he has no proof of Ms Lawson's alleged drug-taking.

Responding to defence barrister Anthony Metzer QC, he said: "Like you, I like proof. I have no proof."

He later said: "I have never, never seen any evidence of Nigella taking any drug whatsoever.

"I want to be helpful, but I genuinely have no real knowledge at all."

When asked by Mr Metzer if he became aware of Ms Lawson's alleged drug-taking around the time of the "Scott's Restaurant incident", he said it was indeed around that time.

Mr Metzer asked if he was "shocked", to which Mr Saatchi said he was.

"I'm very against drugs," he added.

Mr Metzer then said: "You are a friend of Trinny Woodall who feels very strongly about this issue?"

Saatchi rolled his eyes at this question and said: "Yes."

Speaking about Elisabetta, sometimes referred to in court as Lisa, Mr Saatchi said she was "very close" to Miss Lawson.

He said this closeness lasted "throughout the entire period" until the day he received a call from a taxi company about a booking he had not authorised.

"She was exactly like a member of the family, yes," he said.

Mr Saatchi said the "slavery story" - the defendants complained they were "being treated worse than Filipino slaves" - was "nonsense".

When Mr Metzer asked him if he thought a salary of £25,000 was suitably matched to the amount of work Lisa carried out, Mr Saatchi said: "I think it seems perfectly fine."

He then said: "The truth is, there was no real need for us to keep them both on but we both liked them very much and we found work for them."

Mr Saatchi said Miss Lawson was a "very, very nice employer", adding: "The staff all adored her."

He said later: "All I wanted was a nice, happy home atmosphere."

Mr Saatchi told the court that he had a face-to-face conversation with Francesca about how they would pay back the money they spent.

He said he suggested that they be paid half wages and move into a house owned by Ms Lawson in Battersea which she used as a studio.

Mr Saatchi said he thought Francesca saw the idea as "humiliating".

He told the court she said: "I'd rather go to jail than go to Battersea."

He then said she told him: "See you around".

Referring again to the incident outside Scott's, Mr Saatchi said: "I was not gripping, strangling or throttling her. I was holding her head by the neck to make her focus, can we be clear?

"Was it about her drug use? No."

Asked by Mr Metzer, defending Elisabetta Grillo, to explain what he meant in the email he sent to her, Mr Saatchi said: "I was very upset. I wasn't laughing, I was broken-hearted."

He said it was a "terrible, terrible mistake" on behalf of their lawyers that it had been seen more widely.

"Why this went any further than to Nigella - she must have thought there was an agenda she thought this would serve," he added.

Questioned about the drug-taking allegations, Mr Saatchi told the court: "It was hearsay. I personally have absolutely no knowledge that Nigella has ever taken a drug ever.

"I don't like drugs at all and I didn't like reading what the Grillos said was the culture in my house."

Asked if he believed the claims, Mr Saatchi went on: "I may have believed it but I may have been completely wrong and they may have been deluded.

"Like I said, you like proof in this courtroom and I cannot provide proof."

Mr Saatchi described the "Higella" reference as a "silly pun".

He was also asked about why he wrote in the email that his ex-wife now had a "free pass".

Mr Saatchi told jurors: "In one of the very rare conversations I've had with Nigella since we split, I asked her whether she was happy.

"And she said she was happy. And I said 'What was this all about?'

"She said 'I'm happy because I don't feel I have to ask for a pass to do what I feel like doing'.

"And I said to her 'You never had to ask for a pass, you could do whatever you liked. If you wanted to have a girls' night or go to a party then you were free to do so. What do you mean?'

"I was just being nasty," he added.

"This is not a very pleasant email but I was very, very upset.

"What I gathered was now that she was divorced from me she was free to do whatever she wants."

Getting more and more frustrated at Mr Metzer's line of questioning, Mr Saatchi asked him if he expected Ms Lawson to come to court and say she told the defendants they could spend what they liked, and added: "Not a chance."

He also said to Mr Metzer: "You're trying to get me to say something which I'm never going to say."

The court heard that Mr Saatchi's legal representatives sent a letter to Ms Lawson after it seemed that she no longer wished to appear as a witness.

"The purpose of that letter was to say to Nigella 'You cannot just walk away from this trial and see it as my problem because I paid their wages'," he said.

He said the letter "worked" and he withdrew it "the moment it worked".

Under intense questioning from Mr Metzer, Mr Saatchi said he refuted the suggestion that his former wife's mind was so "addled" by drugs that she was not aware what she had or had not permitted the sisters to buy.

"Are you asking me whether I think that Nigella truly was off her head?" he asked.

"Not for a second. Over this whole period she was writing books very successfully and appearing on television shows very successfully."

Mr Saatchi said of Francesca's role: "I don't think it was exactly the most gruelling job in the world."

He described the sisters' jobs as "a fairly flexible way of living".

Mr Saatchi said Francesca had "a completely free range" and said she slept next door to him.

"As far as I was concerned she was very happy with the way we lived," he added.

Recalling when the matter first came to his attention, Mr Saatchi said: "I rather foolishly thought I would overlook it as them getting carried away and being naughty."

He added: "It gives me great pain to see them in this situation."

The multi-millionaire also said he does not spend his days "fussing about even very large sums of money".

Mr Saatchi denied that he told Francesca he would "hunt her and destroy her", or that he banged on a table during a discussion about the expenditure.

Banging his hand down on the surface in front of him, he said: "There was no banging on the table and no threats of any kind.

"I was trying to save her from herself."

He said he was "horrified" that Francesca had given "this rather distasteful story".

Mr Saatchi walked towards a frenzy of waiting cameramen and photographers' flashes as he left the court and made his way to a vehicle.

The case was adjourned until Wednesday when Ms Lawson is expected to appear as a witness.