SNP ministers and MPs threw their weight behind a new Brexit vote after the Electoral Commission said it had concluded that Vote Leave, which featured Boris Johnson and Michael Gove in senior leadership roles, spent almost £500,000 more than it was legally allowed.
The watchdog’s findings prompted claims that the referendum result was invalid and cross-party calls for a public inquiry.
The Scottish Government’s Brexit secretary Michael Russell tweeted that the findings were “damning” and meant it was “essential” to hold a new vote on EU membership.
But a spokesman for Vote Leave rejected the Electoral Commission report, and accused investigators of being “motivated by a political agenda rather than uncovering the facts”.
The elections watchdog found that Vote Leave failed to declare money it spent with data firm Aggregate IQ to target online adverts at potential voters.
Its investigation centred on a donation of almost £680,000 made by Vote Leave to BeLeave, a youth Brexit group.
The Electoral Commission uncovered “significant evidence” of joint working between Vote Leave – which has been fined £61,000 – and another campaign group, BeLeave, founded by student Darren Grimes.
Mr Grimes was fined £20,000 and referred to the Metropolitan Police along with Mr David Halsall, the responsible person for Vote Leave.
Separate campaign groups with their own spending limits are not permitted to co-ordinate strategy. The commission found that BeLeave “spent more than £675,000 with Aggregate IQ under a common plan with Vote Leave”.
This spending took Vote Leave over its £7 million legal spending limit by almost £500,000.
Responding to publication of the Electoral Commission’s report, Mr Russell tweeted: “The result in favour of Brexit was obtained, at least in part, by breaching electoral law. It cannot be allowed to stand – another vote [is] now essential providing there are safeguards for Scotland in terms of possible outcomes.”
The SNP, which has said it would not stand in the way of a bid for a second EU referendum, has suggested any such vote would need to allow for a path towards Scottish independence if the rest of the UK voted again to leave the EU.
SNP MP Joanna Cherry added in her own tweet that the investigation conclusions “undermine the legitimacy of the result” and said: “It’s time to reconsider.”
Bob Posner, the Electoral Commission’s director of regulation and legal counsel, said Vote Leave “refused to co-operate” with the investigation. “The Electoral Commission has followed the evidence and conducted a thorough investigation into spending and campaigning carried out by Vote Leave and BeLeave,” he said. “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.”
Mr Posner 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 co-operate, 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.”
Earlier this month, the former head of the Vote Leave campaign went public with the unpublished interim findings of the Electoral Commission’s investigation, accusing the watchdog of not listening to their account.
The Electoral Commission added that the limit for fines under electoral law of £20,000 per breach is “inadequate for serious offences of electoral or referendum law”.
SNP MP Pete Wishart said the party wanted the maximum fine increased to £1.5m, and called on Scottish Conservative leader Ruth Davidson to account for a donation of £435,000 by a former party chairman to the DUP during the Brexit campaign, some of which was also spent with Aggregate IQ.
Conservative former minister Sir Nicholas Soames said the electoral system should be “blown up and started all over again”, while fellow Tory MP Sarah Wollaston called for a “re-run” of the referendum.
Labour’s Chuka Umunna told MPs that Vote Leave’s actions were an “affront to our democracy”.