The former head of the official "leave" campaign in Britain's 2016 vote on European Union membership denied breaking spending rules on Wednesday ahead of a report from the country's electoral watchdog.
The Electoral Commission has not yet published its report on Vote Leave.
But Matthew Elliott, who headed the group, said the commission has concluded that Vote Leave broke rules by donating more than 600,000 pounds ($800,000) to another group then using the money for its own activities.
Elliott denied wrongdoing, saying Vote Leave acted "both within the letter of the law and also the spirit." He told the BBC that Vote Leave planned to challenge the Electoral Commission report in court.
The commission said it was "unusual" for Vote Leave to issue a public reaction to its initial findings. It said it would publish its full report "at the earliest opportunity."
The watchdog has conducted several investigations into the referendum, which was won by those wanting Britain to leave the EU.
Another pro-Brexit organization, Leave.EU, was fined 70,000 pounds in May for overspending and filing inaccurate records.
The probes have become entangled with inquiries into Facebook's use of users' data because the Brexit campaigns allegedly had contact with the political consultancy Cambridge Analytica, which used data from tens of millions of Facebook accounts to help U.S. President Donald Trump's 2016 election campaign.
Former Cambridge Analytica and Vote Leave staffers have alleged that the group used its undeclared donation to pay a Canadian data firm, Aggregate IQ, for targeted messaging services.
Opponents of Brexit say campaigners' skulduggery may have unfairly influenced the outcome of the June 2016 referendum.