"We 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," Bob Posner, the commission's director of political finance and regulation, said.
According to the commission, Vote Leave group worked with another campaign group, BeLeave, which spent 675,000 pounds. The commission said that Vote Leave was fined 61,000 pounds, while David Halsall, the man responsible for Vote Leave, and Darren Grimes, the founder of the BeLeave campaign group, were referred to the police for false declarations of spending.
The United Kingdom voted to leave the European Union in a referendum in 2016, but the vote left the country divided almost equally into "Remainers" and "Brexiteers."
The model for a future economic partnership and the issue of the border between the Republic of Ireland and Northern Ireland have proved to be the most contentious matters both in the talks with Brussels and the debates within the UK cabinet, which led to the high-profile resignations.