Conservative MP Craig Mackinlay has been acquitted of falsifying his election expenses for his 2015 campaign against then-Ukip leader Nigel Farage.
But senior Tory party official Marion Little, who was said to have effectively run the campaign to fend off the challenge from Mr Farage, was found guilty of two counts of intentionally encouraging or assisting an offence under the Serious Crime Act 2007.
Little’s conviction came after the jury was told “the law was simply abandoned” as the Tories set out to ensure victory over Mr Farage.
He said the only reason she was not going to prison immediately was because she is caring for her husband, who is gravely ill with cancer.
Mr Justice Edis added: “This was a sustained and deliberate course of conduct. Mrs Little acted dishonestly by preparing returns she knew were not completed nor accurate.”
Little was also ordered to pay £5,000 toward the “very substantial” prosecution costs.
South Thanet MP Mr Mackinlay, 52, had been accused of failing to declare more than £60,000 spent on staffing, hotels and advertising.
Prosecutors said he ignored strict spending limits to beat Mr Farage, and told Southwark Crown Court Mr Mackinlay’s victory could have been declared void had the true position been known.
But a jury at Southwark Crown Court acquitted him of two charges of knowingly making a false election expenses declaration under the Representation of the People Act 1983 after deliberating for 53 hours and 29 minutes, having retired on December 5.
Mr Farage told the Press Association: “This verdict shows that there are no election rules for the big parties in British politics, they can wilfully overspend without any consequences.”
Mr Mackinlay’s election agent Nathan Gray, 29, from Hawkhurst, Kent, was earlier acquitted of making a false election expenses declaration.
Mr Mackinlay won in 2015 with a majority of around 2,800 from an electorate of 70,000 and was re-elected to Parliament in 2017 just a week after he was charged.
The prosecution case centred around claims that hotel costs and other expenditure for activists and party workers were recorded as national election spending rather than local, to ensure that strict spending limits for individual candidates were not breached.
During the campaign, South Thanet was visited by a number of high-profile Tory figures, including Theresa May, George Osborne, Boris Johnson and former footballer Sol Campbell.
Declared spending came in under the £52,000 limit set for the constituency, but prosecutors claimed more than £60,000 was not declared.
Mr Mackinlay, from Ramsgate, told jurors his aides had been cautious over the election budget, fearing a challenge by Mr Farage.
“Of any seat in the country, this would be the one looked at and pored over very carefully,” he said.
He insisted he had little control over spending and described a “battle bus” of volunteers drafted in by Conservative Party HQ as a “total waste of time”.
“I was just a small cog in a big gearbox,” he added.
Little, 63, of Ware in Hertfordshire was found guilty of two counts of intentionally encouraging or assisting an offence under the Serious Crime Act 2007 but cleared of a third count.