Vote Leave, the official Brexit campaign, has been fined and referred to the police for breaking electoral law.
The Electoral Commission found that the campaign group, which was backed by top politicians like Boris Johnson and Michael Gove, exceeded its legal spending limit of £7m by almost £500,000 during the 2016 referendum.
In a furious rebuttal, Vote Leave accused the commission of basing its findings on “unfounded claims and conspiracy theories”.
The allegations centre around a £680,000 donation Vote Leave made to the youth-focused campaign group BeLeave.
BeLeave then spent more than £675,000 with data firm Aggregate IQ under a common plan with Vote Leave, something the commission said should have been declared by Vote Leave.
Bob Posner, the Electoral Commission’s director of political finance and regulation and legal counsel, said it had found “serious breaches” of the law.
He added: “We found substantial evidence that the two groups worked to a common plan, did not declare their joint working and did not adhere to the legal spending limits.
“These are serious breaches of the laws put in place by parliament to ensure fairness and transparency at elections and referendums.
“Our findings relate primarily to the organisation which put itself forward as fit to be the designated campaigner for the ‘leave’ outcome.”
Mr Posner said Vote Leave had “resisted” the investigation from the outset.
He added: “It has refused to cooperate, refused our requests to put forward a representative for interview, and forced us to use our legal powers to compel it to provide evidence.
“Nevertheless, the evidence we have found is clear and substantial, and can now be seen in our report.”
The commission also found that Vote Leave filed an incomplete and inaccurate spending report, with almost £234,501 reported incorrectly, and invoices missing for a total of £12,849.99 of spending.
BeLeave founder Darren Grimes has been fined £20,000 after being found to have committed two offences, while Vote Leave has been fined £61,000.
“The commission has now referred both Mr David Halsall, the responsible person for Vote Leave, and Mr Grimes to the Metropolitan Police in relation to false declarations of campaign spending,” its statement added.
The allegations came from information provided by whistleblowers, including the likes of Christopher Wylie and Shahmir Sanni, who claimed the money given to BeLeave was used to pay Aggregate IQ for targeted messaging on Facebook and other social media sites.
A spokesman for Vote Leave said the report contained a “number of false accusations and incorrect assertions that are wholly inaccurate and do not stand up to scrutiny”.
They said the organisation would consider what action to take next, but was confident the findings would be overturned.
The spokesman said: “It is astonishing that nobody from Vote Leave has been interviewed by the commission in the production of this report, nor indeed at any point in the past two years, despite Vote Leave repeatedly making it clear they are willing to do so.
“Yet the commission has interviewed the so-called ‘whistleblowers’ who have no knowledge of how Vote Leave operated and whose credibility has been seriously called into question.
“All this suggests that the supposedly impartial commission is motivated by a political agenda rather than uncovering the facts.
“The commission has failed to follow due process, and in doing so has based its conclusions on unfounded claims and conspiracy theories.”
Mr Grimes hit out at the Electoral Commission in a series of Twitter messages, accusing the organisation of “caving to political pressure from those who despise Brexit”.
As well as support from Mr Johnson and Mr Gove, Vote Leave was backed by Transport Secretary Chris Grayling, International Development Secretary Penny Mordaunt and her predecessor Priti Patel and Brexit Secretary Dominic Raab.
International Trade Secretary Dr Liam Fox, who campaigned for Brexit during the referendum, told Sky News there was “no lack of democratic legitimacy” for the Leave vote and “people knew what they were voting for”.
He said: “We’ve got to stop fighting this referendum over and over again.”
This was echoed by Downing Street, with the prime minister’s official spokesman saying: “We are very clear that this was a legitimate democratic exercise in which the public delivered its opinion and that that is what we’re going to be delivering on,”
From – SkyNews