Momentum, the pro-Corbyn activist group, has been fined £16,700 for multiple breaches of electoral law by the Electoral Commission.
The elections watchdog 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 was set up in 2015 after Jeremy Corbyn became Labour party leader, has been investigated by the commission. The penalties include the highest fine ever 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,” she said.
The Electoral Commission reported that 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.
The group was also 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 recognised it had made “mistakes” in its reporting but said the fines levied by the commission were “disproportionate”.
It said it had 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.”
