The commission's findings came with fines: about $26,270 for Darren Grimes, the founder of BeLeave; and $80,000 for Vote Leave. Both Grimes and Vote Leave campaigner David Halsall have also been referred to the police for allegedly filing false reports about their campaign spending.
"Politicians say they want young people to engage with politics," he wrote. "I was 22 when I got involved in a referendum I felt passionately about. I did nothing wrong."
Vote Leave said in a statement that the commission's report "contains a number of false accusations and incorrect assertions that are wholly inaccurate and do not stand up to scrutiny."
But Bob Posner, director of political finance at the Electoral Commission, said his organization had "found substantial evidence that the two groups worked to a common plan, did not declare their joint working and did not adhere to the legal spending limits."
"These are serious breaches of the laws put in place by Parliament to ensure fairness and transparency at elections and referendums," he said in a statement.
Did overspending affect the outcome of the Brexit vote? That will be difficult to determine. But Shahmir Sanni, a Vote Leave campaigner-turned-whistle-blower told the BBC that the additional money "can make all the difference."
As The Washington Post's William Booth and Karla Adam reported in March, "Sanni said he and Grimes were based in the Vote Leave headquarters; were advised by Vote Leave staffers, including [Prime Minister Theresa] May’s now-senior adviser; and relied on Vote Leave’s attorney, who helped them incorporate the BeLeave group."
Lawmaker Chuka Umunna told Parliament on Tuesday that "we cannot say with confidence that this foul play did not impact on the result.”
The day after Davis resigned, Foreign Secretary Boris Johnson also stepped down, criticizing May's Brexit strategy and saying "[the Brexit] dream is dying, suffocated by needless self-doubt." Johnson was a key Vote Leave campaigner, and on Tuesday, members of the Labour Party called for investigations into both him and Environment Minister Michael Gove, who also backed the Vote Leave campaign.