Britain's official Brexit campaign, Vote Leave, has been fined for breaking spending rules in the 2016 EU membership referendum, the Electoral Commission said Tuesday, adding that it had referred the case to the police.
The Electoral Commission said the winning side in the referendum had worked together with a smaller pro-Brexit group called BeLeave to get around campaign finance rules.
"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," said Bob Posner, the commission's director of political finance and regulation.
"These are serious breaches of the laws put in place by parliament to ensure fairness and transparency at elections and referendums," Posner said.
A Vote Leave spokesman accused the Electoral Commission of being "motivated by a political agenda rather than uncovering the facts".
The spokesman said there were "a number of false accusations and incorrect assertions that are wholly inaccurate and do not stand up to scrutiny".
The report found that the Vote Leave campaign exceeded its legal spending limit of £7.0 million (7.9 million euros, $9.3 million) by almost £500,000.
Vote Leave, which had support from leading eurosceptic Boris Johnson, also returned an incomplete and inaccurate spending report and failed to submit some invoices for its spending.
The report said the BeLeave group, which was founded by fashion student Darren Grimes, spent more than £675,000 with Aggregate IQ, a Canadian digital political advertising company, under a "common plan" with Vote Leave.
The company was mentioned in the scandal over Cambridge Analytica, a now defunct British company accused of misusing data obtained from Facebook to micro-target political ads.
Christopher Wylie, a Cambridge Analytica whistleblower, alleged that pro-Brexit groups worked together to get around campaign finance rules by using the services of Aggregate IQ.
Wylie said that Aggregate IQ was linked to Strategic Communication Laboratories (SCL), the parent company of Cambridge Analytica.
The Electoral Commission said it had referred the case to police.
"Investigation files have been shared with the Metropolitan Police in relation to whether any persons have committed related offences which lie outside our regulatory remit," the report said.
Vote Leave was fined £61,000 and Grimes was fined £20,000, the maximum levy for an individual.
But the Vote Leave spokesman said it had provided evidence to the Electoral Commission "proving there was no wrongdoing.
"And yet, despite clear evidence of wrongdoing by the Remain campaign, the commission has chosen to ignore this and refused to launch an investigation."
"We will consider the options available to us, but are confident that these findings will be overturned," he said.