The Electoral Commission will not investigate the Democratic Unionist party over claims it coordinated its Brexit referendum campaign spending with Vote Leave in order to break legal spending limits.

The Northern Irish party, which props up Theresa May’s government in the Commons, had faced a series of allegations about its spending during the 2016 EU referendum, after it spent hundreds of thousands of pounds campaigning to leave the bloc.

The DUP’s referendum spending was aided by a £435,000 donation from unknown individuals, channelled through an organisation run by a former Scottish Conservative parliamentary candidate. The original source of the donation remains unclear, as until recently the law did not require political parties in Northern Ireland to declare their financial backers.

The DUP then spent most of its money campaigning outside Northern Ireland, including buying a £280,000 advert in the Metro newspaper, which is only distributed in Great Britain.

The party also paid for targeted Facebook advertising through AggregateIQ, at that time an obscure Canadian social media business, which was at the centre of the illegal campaign coordination between Vote Leave and the campaign group BeLeave, run by the young campaigner Darren Grimes.

The Electoral Commission considered the DUP allegations after they were made in a BBC investigation, which alleged the party’s pro-Brexit activity was conducted as part of a common campaign with Vote Leave – enabling the pro-Brexit lobbying group to break spending limits.

The regulator has now concluded it “does not have grounds to open an investigation” because it does not have sufficient evidence. A spokesperson confirmed there were no other ongoing investigations into DUP activities during the referendum.

The commission has also rejected claims from the Tory MP Priti Patel that the official remain campaign should be investigated for allegedly coordinating spending between various pro-EU groups during the referendum.

“After a thorough assessment, our conclusion is that we can find nothing beyond conjecture to support the argument that there must be undeclared joint spending between these various [remain] campaigners,” said Louise Edwards, head of regulation at the organisation. “There is nothing we can point to that reasonably indicates some kind of common campaign activity.”

Edwards said there had to be clear evidence of one pro-EU group directing another on how to spend money in order to prompt an investigation. She said it was legal for campaigners to “use the same suppliers and the same volunteers”, while donors are legally allowed to give to more than one campaign group working for the same cause.

However, the Electoral Commission concluded that it would investigate a campaign group called Wake Up And Vote after finding there was “reasonable suspicion” that it may have coordinated its spending with an ad agency to produce a series of videos featuring actors Lily Cole, Keira Knightley and Dominic Cooper urging people to vote.



In May the Electoral Commission fined Leave.EU, the pro-Brexit campaign group founded by Arron Banks, £70,000 after finding that it had breached multiple counts of electoral law.



Pro-Brexit campaigners have increasingly turned their anger on the commission itself following its ruling against the activities of Leave.EU and Vote Leave. One activist who was fined £250 as part of the investigation into Brexit spending, on Thursday released a film of himself paying the penalty in cash, which he dumped on the floor in the foyer of the Electoral Commission’s central London office.



The commission also told Patel, a former cabinet minister, that they were exasperated by the attacks on the organisation’s neutrality with regards to Brexit: “It would be wrong for us to take decisions on the basis that we must balance action in respect of ‘leave’ campaigners with action in respect of ‘remain’ campaigners. That would undermine our neutrality, rather than ensure it.”