Brexit campaign group Vote Leave has been fined £61,000 and referred to the police after an Electoral Commission probe said it broke electoral law.

The investigation found "significant evidence of joint working" between the group and another organisation - BeLeave - leading to it exceeding its spending limit by almost £500,000.

Vote Leave also returned an "incomplete and inaccurate spending report", with almost £234,501 reported incorrectly, and invoices missing for £12,849.99 of spending, the watchdog said.

BeLeave founder Darren Grimes has also been fined and referred to the police for breaking the group's spending limit by more than £665,000 and wrongly reporting the spending as his own.

Veterans for Britain were also found to have inaccurately reported a donation it received from Vote Leave and has been fined £250.

'Refused to cooperate'
Bob Posner, from the Electoral Commission, said: "The Electoral Commission has followed the evidence and conducted a thorough investigation into spending and campaigning carried out by Vote Leave and BeLeave.

"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."

He added: "Vote Leave has resisted our investigation from the start, including contesting our right as the statutory regulator to open the investigation. 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."

Vote Leave was the officially designated campaign group for Leave in the UK's referendum in 2016 into whether or not the UK should stay in the European Union.

The result of the referendum was 51.9% for Leave and 48.1% for Remain. The UK is due to officially leave the European Union at 23:00 GMT on 29 March, 2019.

'Motivated by political agenda'
A Vote Leave spokesman said: "The Electoral Commission's report contains a number of false accusations and incorrect assertions that are wholly inaccurate and do not stand up to scrutiny.

"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. 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.

"Vote Leave has 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.

"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.

"We will consider the options available to us, but are confident that these findings will be overturned."