Arron Banks has claimed there was no Russian interference in the pro-Brexit campaign.
In a staunch denial of any wrongdoing in the 2016 referendum, Leave.EU co-founder Mr Banks told the Andrew Marr Show: "There was no Russian money and no interference of any type. I want to make that clear."
But he told the BBC presenter on Sunday that the source of the £8million funding - the biggest political donation in UK electoral history - was insurance company Rock Services.
He said: "The money came from a UK-registered company [which he claims to be Rock Services], it was generated from cash, generated from businesses in the UK and the whole misunderstanding revolves around the role of Rock Holdings as a holding company.
"I'd just like to say, absolutely for the record, there was no Russian money and no interference of any type. I just want to be absolutely clear about that."
Asked again where the money came from, Mr Banks repeated: "The money came from Rock Services, which is a UK-limited company. It was generated out of insurance written in the UK and contrary to some press reports, we insure nearly half a million customers a year, the size of Manchester. It's a sizeable business.
"I'm telling you it came from insurance business written in the UK.
"I'm confused with the Electoral Commission referring this to the police. We've not been asked by the Electoral Commission to produce our bank statements."
The investigation into Mr Banks was launched after the elections watchdog said it had reasonable grounds to suspect he was not the true source of the cash.
But he insisted: "We have an insurance business [Rock Services] which generates a large amount of cash, £20m to £25m a year. The money from Rock Services went to Leave.EU."
There had been a row over Mr Banks' appearance on the show, with prominent Remainer Lord Adonis writing to Lord Hall, the director general of the BBC, to say the invite was a "serious editorial misjudgement".
In the heated exchange, Mr Banks told Mr Marr: "You just want to smear me, yeah you do." In another jibe, he said: "I think I know business affairs better than you."
He claimed the investigation was about "undermining Article 50, undermining the Brexit result, and it's a collection of very vicious Labour MPs who have grouped together with the Guardian and Financial Times to try to undermine Brexit". He added: "We know the Electoral Commission has got a bias on this."
He was also asked why he wrote to constituents of Damian Collins - chairman of the digital, culture, media and sport committee - calling him a "snake in the grass". He replied: "Well he is."
And questioned about a report in the Sunday Times that he would back Remain if the 2016 referendum were re-run, he replied: "What I said was that 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."
