The left-wing activist group Momentum has been fined £16,700 for “multiple breaches” of electoral law, the Electoral Commission has said.
The commission said the fines related to an inaccurate spending return for the 2017 general election as well as failures to report donations.
It is the first time the group – which backs Jeremy Corbyn – has been investigated by the commission and the penalties include the highest fine to be levied on a non-party campaigner for not submitting a complete and accurate spending return.
Louise Edwards, director of regulation at the commission, said: “Non-party campaigners are essential for a healthy democracy. But just as crucial is that after a poll, voters can see complete and accurate spending data.
“The fines that we have levied reflect Momentum’s repeated revisions to their spending return, poor record keeping and failure to follow advice given by the commission prior to the election.”
In its report, the commission said the group had been fined £12,150 for its failure to submit a complete and accurate spending return for the general election.
It was fined a further £2,700 for the omission of £22,958.46 of reportable donations from a post-poll donation report.
It was fined £250 for failing to provide the required declaration to accompany their post poll donations report and £250 for failing to provide all required invoices with their spending return.
The group has also been ordered to pay £1,350 in relation to its failure to report two donations for the Transport Salaried Staffs Association totalling £18,000 within the required time limit.
Momentum acknowledged that it had made “mistakes” in its reporting but said the fines levied by the commission were “disproportionate”.
It said it had now put in place “comprehensive systems and processes” to ensure that it complied with the regulations in future.
“The Electoral Commission did find some mistakes in our reporting and some clerical errors. This isn’t surprising for a new organisation which at the time was less than two years old and had 25,000 members and 150 local groups,” said Momentum spokeswoman Laura Parker.
“The Conservatives likely employ more lawyers than Momentum have staff, and even getting close to fully complying with these complex regulations for a volunteer led, social movement organisation is a herculean task.
“We’re proud to be funded by small donations and powered by tens of thousands of volunteers, and we believe that our democracy should serve the many. These laws only help big corporate donors who want to funnel dark money into our political system.”
She added: “We also believe the fines levelled are disproportionate. The fines and associated staff time will cost Momentum more than our entire regulated campaign spend during the election.
“Not only did Momentum cooperate fully with the Electoral Commission, but these offences are incredibly minor when compared with other political organisations.”
Ms Edwards said: “Non-party campaigners that seek to persuade people to vote a certain way rightly have legal obligations; it is incumbent on them to invest properly in having the right processes and staff to meet their obligations.
“Momentum is unlike most non-party campaigners in that political campaigning is its full-time work, so it is particularly disappointing that they have failed to meet the law’s requirements.”