LONDON (AP) — Britain's National Crime Agency is investigating one of the leaders of the campaign to take Britain out of the European Union over suspected illegal campaign funding during the country's EU membership referendum.

The Electoral Commission says wealthy businessman Arron Banks, his group Leave.EU "and other associated companies and individuals" are subject to a criminal investigation. The inquiry concerns 8 million pounds ($10.3 million) reportedly loaned or given by Banks to a pro-Brexit group.

The commission says it suspects Banks "was not the true source" of the money and that it really came from an offshore company.

The crime agency confirmed Thursday it is investigating but said it could not discuss "any operational detail."

Banks said he was confident a "full and frank investigation" would clear him.