Momentum is to be investigated by the Electoral Commission over its role campaigning for Labour during the 2017 general election, including whether it breached campaign spending rules.
The leftwing grassroots movement, which sprang up in support of the Labour leader, Jeremy Corbyn, has been given much of the credit for the party’s success in the June election, during which it deployed thousands of activists and volunteers in key marginal seats.
The commission said it would look at whether Momentum had breached spending limits for an unauthorised, non-party campaigner, and that any contravention risked damaging voters’ confidence in the result of the poll.
It would also examine whether Momentum submitted a return or declaration with inaccurate donation information, and whether that return was complete and included all invoices for payments of more than £200.
In a statement on Thursday, the commission said it was possible contraventions or offences of a different nature could be found during the investigation.
Bob Posner, the commission’s director of political finance and regulation, called Momentum a “high-profile campaigning body” during the June election.
“Questions over their compliance with the campaign finance rules at June’s general election risk causing harm to voters’ confidence in elections,” he said. “There is significant public interest in us investigating Momentum to establish the facts in this matter and whether there have been any offences.
“Once complete, the commission will decide whether any breaches have occurred and, if so, what further action may be appropriate, in line with its enforcement policy.”
During general elections, strict rules govern the spending and activities of campaigns that are not run by political parties but are intended to influence people to vote a particular way.
In the 12 months leading up to the election, groups can campaign for people to vote for one particular political party – known as “targeted spending” – within certain limits: £31,980 in England, £3,540 in Scotland, £2,400 in Wales, and £1,080 in Northern Ireland.
In November, Momentum said it had spent £38,743 on the general election campaign. The World Transformed, a leftwing grassroots festival closely associated with the group, said it had spent £60,590.
Campaigning organisations may be allowed to spend more than the legal limit but need the authorisation of the party they are campaigning to elect. If a party gives permission, the campaign can use extra funds but that will count towards that political party’s own legal spending limit.
A Momentum spokesperson said much of the investigation referred to “administrative errors that can be easily rectified.”
“Momentum put a lot of effort and resources into detailed budgeting and financial procedures during the election to ensure full compliance,” the spokesman said. “Our election campaign was delivered on a low budget because it tapped into the energy and enthusiasm of tens of thousands of volunteers across the country.
“We have a good working relationship with the Electoral Commission, and will fully comply with the investigation going forward.”
All political parties and campaigns have come under commission scrutiny in recent years. Labour was fined £20,000 for undeclared spending in the 2015 election, including on the infamous “Ed Stone” which laid out the campaign pledges of the then Labour leader, Ed Miliband.
The Conservatives were fined a record £70,000 for “significant failures” in reporting its campaign spending from 2015.
The commission is currently investigating the official Vote Leave campaign’s activities during the referendum.