LONDON (Reuters) - Britain’s electoral regulator misinterpreted the spending law when it allowed the main Brexit campaign to donate to a smaller, aligned group during the 2016 referendum campaign, London’s High Court ruled on Friday.

Pro-EU demonstrators protest outside parliament in Westminster London, Britain, September 13, 2018. REUTERS/Henry Nicholls

Britain’s officially designated Brexit campaign group, Vote Leave, said the Electoral Commission had told the group it could donate to other Leave campaigners without having to count it against its own referendum expenses.

But the High Court found that the Electoral Commission “misinterpreted the definition of ‘referendum expenses’” in a way which was “inconsistent with both the language and the purpose of the legislation” in giving the advice.

Jo Maugham, a lawyer and campaigner on the winning side of the case, said the decision was “coruscating” for the Commission, and that the main Remain campaign had not been given the same rights to make donations.

“What is now clear is that the Electoral Commission unlawfully tilted the playing field in the Referendum,” he said in a statement.

Vote Leave was separately fined by the Electoral Commission in July for co-ordinating its activities with the smaller campaign group, BeLeave, to pay digital services from Aggregate IQ, thereby exceeding spending limits. The campaign group refuted the findings.

The Electoral Commission said Friday’s ruling showed the court had backed up its July findings.

“The Court arrived at the same conclusion as the Commission did in its investigation - that Vote Leave should have accounted for the expenditure on the digital services firm, Aggregate IQ – although it found an additional reason for reaching that conclusion,” the regulator said in a statement.

But Vote Leave Chief Executive Matthew Elliott said the court’s ruling undermined the Electoral Commission’s earlier finding, adding that the campaign group would not have made the donation if they had not been advised that they could.

“The Electoral Commission’s defeat in the High Court today has thrown electoral law for future elections and referendums into total chaos,” he said in a statement.

“Either the Electoral Commission is wrong or the High Court is wrong.”