His lawyer told the High Court that a private prosecution over claims that the UK pays the EU £350m a week was “politically motivated and vexatious”.

Adrian Darbishire QC said the district judge who summonsed the former foreign secretary to court last month had “erred in law” when reaching her decision.

“It was just a political claim open to and available for contradiction and debate, and it was, and is, for the good sense of the electorate to discount it if they choose so to do,” the lawyer added.

“It is not for the Crown Prosecution Service, judge and jury to determine the misconduct of this claim and it is not for the interested party either.”

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Giving the court’s decision, Lady Justice Rafferty said: “We are persuaded, Mr Darbishire, so you succeed, and the relief that we grant is the quashing of the summonses.”

The High Court judge said reasons for her ruling, alongside Mr Justice Supperstone, would be given in detail at a later date.

Mr Johnson is currently the bookies’ favourite to become leader of the Conservative Party and succeed Theresa May as prime minister, and his political supporters had condemned a judge’s decision to summons him for a potential criminal trial.

Leadership rival Sajid Javid said he was “very glad” to see the case thrown out, adding: “Freedom of speech feels increasingly challenged – we should always seek to debate political arguments in the open rather than close them down.”

Marcus Ball, 29, had raised more than £300,000 through crowdfunding campaigns in order to lodge a private prosecution against Mr Johnson.

Speaking outside court, Mr Ball said he would decide if he would launch an appeal against the High Court’s ruling after seeing the full reasons for their decision.

“We have just given the green light for every politician to lie to us about our money forever,” he added. “That is a terrifying idea.”

Asked if he had a message for Mr Johnson, Mr Ball said: “You don’t have the right to lie to the public about how their money is being spent. I would ask you, please, all members of parliament, all elected representatives, understand: you cannot lie to the public about their money.”

Boris Johnson facing legal action over £350 million Brexit bus claim

A Westminster Magistrates’ Court hearing last month said that Mr Johnson “used the platforms and opportunities offered to him by virtue of his public office” to endorse claims that EU membership was costing the UK £350m a week.

Lewis Power QC, a lawyer representing Mr Ball, told the court Mr Johnson had deliberately misled the public during the EU referendum campaign and then repeated the statement during the 2017 general election.

“Democracy demands responsible and honest leadership from those in public office,” he added. “The conduct of the proposed defendant Boris Johnson was both irresponsible and dishonest. It was, we say, criminal.”

Mr Darbishire said his client denied acting dishonestly and claimed Vote Leave’s £350m-a-week claim – which was displayed on the side of a bus – was based on information that was “freely available to all”.

On 29 May, District Judge Margot Coleman threw out his argument that the case was a “vexatious” attempt to undermine the result of the 2016 referendum, and found there was “prima facie” evidence of potential misconduct in a public office.

Speaking to reporters before Friday’s hearing, Mr Ball said: “I’ve spent three years of my life working ridiculous hours for, per hour I believe, the minimum wage to bring this case because I believe in the merits of it. Somebody who was doing this to create a stunt would not act like that.”

The £350m figure was emblazoned on the red campaign bus used by Vote Leave during the referendum, with the slogan: “We send the EU £350m a week, let’s fund our NHS instead.”

A lawyer for the man who brought the prosecution said there was ‘significant public and political interest’ in the issue (Getty)

Mr Darbishire QC told the High Court that the figure was disputed ”as soon as it was said“ and remains the subject of public debate.

“In drawing upon freely-available public statistics for the purpose of a political argument, Vote Leave, and those who supported and spoke for that campaign, were clearly not acting as public officials, nor exercising any public power,” he added.

“They made no claim to special knowledge of the sums expended by the UK, they exercised no official power in promoting that message, and the assessment and publication of the level of the UK’s total EU spending formed no part of Mr Johnson’s official duties.”

Mr Darbishire said the offence of misconduct in public office had never been used for statements made in political debate, adding: “It is abundantly clear that this prosecution is motivated by a political objective and has been throughout.”

A lawyer representing Mr Ball told the High Court there was “ample evidence that Mr Johnson did know [£350m a week] was a false and misleading figure”.

Jason Coppel QC said the issue was of “significant public and political interest which has been heightened by recent political events – including the candidacy of the claimant for leadership of the Conservative Party”.

“But that does not establish that the motivation of the interested parties as prosecutors is improper, whether because it is a purely political motivation or otherwise,” he added.

“The entirely proper motivation for the prosecution is to hold to account a high-profile politician and holder of public office for what is alleged to be significant misconduct in relation to an issue of great public importance.”