Nigella Lawson said she was "disappointed but unsurprised" by the acquittal of her former personal assistants on fraud charges, adding that her experience as a witness was "deeply disturbing".

The TV cook said the jury was "faced with a ridiculous sideshow of false allegations" about drug use that made focus on the actual criminal trial impossible.

Francesca Grillo, 35, and her sister, Elisabetta, 41, were found not guilty of one count each of defrauding Ms Lawson and her ex-husband, Charles Saatchi.

Ms Lawson admitted during the three-week trial that she had taken cocaine, after allegations of drug use arose as part of the defence case.

But Scotland Yard said today that it would not be investigating unless new evidence comes to light.

Ms Lawson said in a statement: "When false claims about habitual drug use were introduced, I did everything possible to ensure the CPS (Crown Prosecution Service) was aware of the sustained background campaign deliberately designed to destroy my reputation."

During the trial she had accused multi-millionaire art dealer Mr Saatchi of threatening to "destroy" her.

She said that, despite doing her civic duty, she was "maliciously vilified without the right to respond".

The Italian sisters had been accused of using company credit cards, spending hundreds of thousands of pounds on designer goods for themselves while working as personal assistants to the celebrity couple.

They claimed every purchase had been approved by their then-bosses.

The trial could have collapsed after British Prime Minister David Cameron declared his support for "Team Nigella" in a magazine interview halfway through the trial.

His comments prompted the defence calling for the trial to be brought to an end.

After a day of drama and tension at Isleworth Crown Court in west London, during which Elisabetta collapsed upon arrival, the younger sister was delighted to learn of the not-guilty verdicts.

Neither woman had been in Court 8 when the jury foreman read out the verdicts, the seven men and five women having been deliberating for almost nine hours.

The pair had been excused from the dock because Elisabetta stopped breathing following a panic attack yesterday and spent two hours in hospital last night.