Nigella Lawson attacked the "ridiculous sideshow" of allegations about drug use levelled against her during the trial of her former personal assistants, after they were found not guilty of a £685,000 fraud on the accounts of her and her former husband.

Her statement was a bitter conclusion to a three-week court case in which the self-styled "domestic goddess" chose to admit taking cocaine on seven occasions as she gave evidence against Elisabetta and Francesca Grillo, who had been accused of spending lavishly on family credit cards without the permission of her or her husband of 10 years Charles Saatchi.

Lawson, 53, who is due to return to British TV screens in a Channel 4 food talent show on 7 January and now faces a reputation rebuilding exercise, complained in a statement after the verdict of being "maliciously vilified" and of a "sustained background campaign deliberately designed to destroy my reputation".

The not guilty verdict was handed down by the jury of seven men and five women after eight hours and 52 minutes of deliberation. The jury had heard claims from the Grillo sisters that the use of cocaine and cannabis was rife in the Lawson home as part of a defence aimed at showing a household that was out of control.

Repeating the rebuttal she had made in court, Lawson said after the verdicts that she found her experience as a witness "deeply disturbing", adding: "During the trial not one witness claimed to see me take drugs and not one of my three assistants was asked about these claims by the defence, despite being cross-examined at length.

"I did my civic duty, only to be maliciously vilified without the right to respond. I can only hope that my experience will highlight the need for a reform that will give witnesses some rights to rebut false claims made against them."

The jury at Isleworth crown court had heard a story of collapsing marriage, in which Lawson said she had been subject to acts of "intimate terrorism" by Saatchi – and free spending in the household where a "huge stash" of cash was kept on the fridge. Annual spending on household credit cards was as high as £1.2m.

The acquittal of the sisters sparked emotional scenes in the court corridors. Elisabetta Grillo, 41, who had suffered a series of panic attacks and collapsed in the dock on Thursday afternoon, wept with relief while Francesca Grillo, 36, hugged her solicitor. "My God, I am just shaking," she said. "We can go home." Her barrister, Karina Arden, called out in Italian C'e un Dio ("there is a God"). Grillo repeated the phrase, smiling broadly.

Outside court the sisters' solicitor, Richard Cannon, said they would not comment but were relieved at the verdicts. He said: "This has been a long, hard fight, played out in the gaze of the world's media." The sisters' representatives were in negotiations with the Daily Mail, the Mail on Sunday and the Sun last night for the sale of rights to their story – bringing the prospect of further domestic revelations.

There was one crumb of comfort for Lawson when a spokesman for the Metropolitan police said the force would not investigate allegations of class A drug use by her – unless " any evidence, and that includes material from the trial, that could be investigated come to light".

The high society fraud case had gripped the nation and even David Cameron came out as a supporter of "Team Nigella"– a move that came close to causing the trial to collapse. Lawyers for the Grillos applied for the trial to be stayed because the intervention was an abuse of process after the prime minister had described her as a "very funny and warm person" and said he was "a massive fan". Judge Robin Johnson criticised the "regrettable" intervention. In the hours after the verdict, a chastened Cameron demonstrated that he had recognised the severity of the rebuke. When asked if he was pleased by the outcome, he said: "I've probably said enough about this, so I'll take the fifth."

The verdict creates a fresh danger for Lawson, said Mark Borkowski, a PR expert. "There will be people in the media working on this to find out what is the truth and if the [drug] claims can be stood up," he said. "There is a danger there ... Whichever way you look at it it isn't good. But Nigella has powerful friends, many of whom are journalists. She can turn to Team Nigella and there is a lot of sympathy."

Lawson told police before the trial alleging Saatchi had "used his best endeavours to encourage press and media to publish untrue stories about me". She also said in court that her former husband had threatened to "destroy" her if she did not give evidence in the case. He had told her in an email that he believed the Grillos' claims that she was "off her head on drugs" – but later, when giving evidence, he said he no longer believed this was the case and was "bereft" that the email had emerged.

Lawson's team is understood to be concerned Saatchi may still pursue her with a civil claim. A month before the trial, he threatened her with civil action to recoup unauthorised spending by their personal assistants, a claim that could rise towards £1m. Saatchi's lawyers, Rollingsons, said he could hold her responsible for the losses on the basis of her alleged negligence in failing to monitor the accounts. A lawyer representing Saatchi declined to comment.