Vote Leave broke the law during the EU referendum by exceeding legal spending limits, a Brexit activist has claimed.
Shahmir Sanni told Channel 4 News that the official Brexit campaign used a different group, BeLeave, to overspend.
Vote Leave chief Dominic Cummings has already denied the claim and said he checked with the Electoral Commission before donating money to the group.
Mr Sanni has also criticised Vote Leave manager Stephen Parkinson, his ex-boyfriend, for outing him as gay.
“I know that, that Vote Leave cheated… I know that, that people have been lied to and that the referendum wasn’t legitimate,” Mr Sanni told Channel 4 News.
BeLeave was set up to give young pro-Brexit campaigners a voice during the referendum.
Separate campaign groups could spend up to £700,000 if they registered as permitted participants.
Observer/C4 story utterly ludicrous, #VoteLeave won fair & square – and legally. We are leaving the EU in a year and going global #TakeBackControl #GlobalBritain
— Boris Johnson (@BorisJohnson) March 24, 2018
End of Twitter post by @BorisJohnson
In a blog on Friday, Mr Cummings denied allegations of links between his campaign and Cambridge Analytica and said the claims were “factually wrong, hopelessly confused, or nonsensical”.
Lawyers for AIQ told Channel 4 News that it had “never entered into a contract with Cambridge Analytica” and it had “never knowingly been involved in any illegal activity”.
In a “personal statement” issued to Channel 4 News, Stephen Parkinson denied the allegations and said he was confident he had stayed within the law and spending rules “at all times”.
He said he was “saddened” by the “factually incorrect and misleading” statements from Mr Sanni, who now works for the Taxpayer’s Alliance.
Earlier, Mr Sanni said – in a statement issued through his lawyers – that Mr Parkinson had outed him as gay in his original response.
Mr Sanni, a British Pakistani, said he was forced to tell his family and that relatives in Pakistan could be in danger as a result.
“The idea… that the campaign was legitimate is false.” A Brexit insider accuses Vote Leave of cheating – in response the PM’s political secretary denies the claims and “outs” the accuser as gay. #TheBrexitWhistleblower https://t.co/NWMQSmElof pic.twitter.com/uM8koUk7Ta
— Channel 4 News (@Channel4News) March 24, 2018
End of Twitter post 2 by @Channel4News
In his original statement, published on Mr Cummings’ blog on Friday, Mr Parkinson said he dated Mr Sanni for 18 months, before splitting up in September 2017.
“That is the capacity in which I gave Shahmir advice and encouragement, and I can understand if the lines became blurred for him, but I am clear that I did not direct the activities of any separate campaign groups,” he said.
Mr Grimes told Channel 4 News he denied the allegations.
A solicitor for Vote Leave told the programme the campaign had been cleared twice on this issue by the Electoral Commission.
The Electoral Commission said: “The commission has a number of investigations open in relation to campaigners at the EU referendum; it does not comment on live investigations.”
Green Party joint leader Caroline Lucas told the BBC’s Andrew Marr Show: “This is a really complex network – but big, big questions need to be asked and it goes much wider than just the referendum.”
But Brexit campaigning Tory MP John Redwood told Sky News Vote Leave had twice been cleared of breaching the rules.
He added: “If it’s got to be investigated again, well then, so be it. But I think most people out there feel we had a perfectly fair referendum.”