Mr Banks has faced claims that money to fund Leave.EU came from Russian sources - something he has repeatedly denied.
The Electoral Commission has referred Banks, his campaign Leave.EU, its parent organisation Better for the Country, and "other associated companies and individuals" following its investigation into the 2016 campaign, which focused on a reported £2 million loan to Better for the Country from Banks and his group of insurance companies.
Bob Posner, the commission's director of political finance, said: "We have reasonable grounds to suspect money given to Better for the Country came from impermissible sources and that Mr Banks and Ms Bilney, the responsible person for Leave.EU, knowingly concealed the true circumstances under which this money was provided".
The Electoral Commission has said it suspects the cash instead came via another company called Rock Holdings, which is incorporated in the Isle of Man.
When pressed on the source of the funding, Banks told the BBC that the cash in question was generated by Rock Services, a UK-listed company, that created the funds through insurance business in the UK.
"Contrary to some of the press reports in the Financial Times and other Remain-leaning publications, we insure almost half a million customers a year - the size of Manchester".
"If Rock Services made the donation, where did the money come from for Rock Services to do that?"
We employ 1,000 people and we turn over £250m of premium a year.
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Banks raised eyebrows further when he suggested that if given the time again, he would vote to remain in the EU.
Andrew Adonis, a leading remain campaigner, said in a letter to the BBC that Banks's expected appearance was the result of "a very serious editorial misjudgment, influenced by a culture of accommodation to extreme Brexiteers now deeply embedded within the BBC".
"It's a group of vicious MPs who have grouped together with the Guardian and the FT".
Well, details of that were revealed by Facebook earlier this year when they released a string of pro-Brexit adverts that popped up on voters' feeds before the European Union referendum in June 2016.
Mr Banks lashed out again at the Electoral Commission, accusing it of being full of his political opponents, as well as elements of the media who opposed Brexit.
Mr Banks was asked by Andrew Marr why he wrote to Mr Collins' constituents calling him a "snake in the grass".
Mr Collins responded to the letter last week by saying he was "not going to be intimidated out of doing my job" by Mr Banks.
Both Bilney and Banks deny any wrongdoing, with the latter posting a flurry of tweets on Friday evening.