Arron Banks has insisted there was “no Russian money” involved in the over £8m of campaign funding made during the Brexit referendum.
The founder of Leave.EU is the subject of a National Crime Agency (NCA) probe into the source of payments.
Speaking to the BBC’s Andrew Marr Show on Sunday, Banks said the money had all been from his UK-registered firm.
“There was no Russian money and no interference of any type. I want to be absolutely clear about that,” he said.
“The money came from Rock Services which was a UK limited company, it was generated out of insurance business written in the UK.”
He accused “vicious MPs” and journalists of trying to undermine the Brexit process.
The NCA investigation was launched last week after the Electoral Commission said it had reasonable grounds to suspect Banks was not the true source of the cash.
Bob Posner, the commission’s director of political finance, said the elections watchdog suspected the money came from “impermissible sources”.
Banks also told Marr he would vote to stay in the EU if the referendum were to happen again.
“The corruption I have seen in British politics, the sewer that exists and the disgraceful behaviour of the government over what they are doing with Brexit and how they are selling out, means that if I had my time again I think we would have been better to probably Remain and not unleash these demons,” he said.
The Electoral Commission’s review of referendum finances focused on £2m reported to have been loaned to Better for the Country by Banks and his insurance companies and a £6m donation he made alone.
It said that, as well as having reasonable grounds to suspect he was not the true source of the cash, loans involved a company, Rock Holdings, based on the Isle of Man, which was impermissible under the rules.