UK National Crime Agency investigating Brexit-backer Arron Banks

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.

"This follows our acceptance of a referral of material from the Electoral Commission," the NCA said.

"While electoral law offences would not routinely fall within the NCA’s remit, the nature of the necessary inquiries and the potential for offences to have been committed other than under electoral law lead us to consider an NCA investigation appropriate in this instance."

Banks, who ahead of the 2016 Brexit referendum financed Leave.EU, a campaign led by Nigel Farage, then the leader of the UK Independence Party, has faced questions in parliament about the source of his wealth.

He has repeatedly denied any wrongdoing.

Arron Banks on Thursday welcomed a National Crime Agency (NCA) investigation and added that he had never received any foreign - or Russian - funding for one of the main campaigns for Britain to leave the EU.

"We welcome this investigation as it is an opportunity for us to clear up the matter," Banks told Reuters. "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."

"The electoral commission have said offences may have been committed but have provided no evidence," Banks said. "As usual the Electoral Commission is batting for the Remainers in parliament."