The UK National Crime Agency (NCA) said on Thursday it had started an investigation into British businessman Arron Banks, who financed one of the main campaigns for Britain to leave the EU.
Banks, who was pictured with Donald Trump and leading Brexiteer Nigel Farage outside a gilded elevator soon after Trump's 2016 U.S. presidential election victory, said he welcomed the investigation.
"It is an opportunity for us to clear up the matter," Banks told Reuters.
"The Electoral Commission have said offences may have been committed but have provided no evidence."
Banks said he had written to Prime Minister Theresa May to ask for an investigation.
The National Crime Agency, which investigates serious and organised crime, said the investigation comes after an referral from the Electoral Commission but will extend to offences other than breaking electoral law.
Banks, who ahead of the 2016 Brexit referendum financed Leave.EU, a campaign led by Farage, then the leader of the UK Independence Party, has faced questions in parliament about the source of his wealth.
"Rock holdings is a company I own and control and I'm a U.K. tax payer, no Russian or foreign money has ever come into it," Banks said.