London - Multi-millionaire Brexit backer Arron Banks is under investigation over campaign spending at the 2016 EU referendum, the Electoral Commission has said.
The commission opened the probe to establish whether Banks and his company "Better for the Country Limited" (BFTCL), which donated to pro-Brexit campaigns, breached electoral finance rules.
The investigation will look into whether the company was the true source of donations made in its name, and whether Banks was the true source of loans reported by a referendum campaigner in Banks's name.
"It is possible that during the course of our investigation we will identify potential contraventions and/or offences under the Political Parties, Elections and Referendums Act 2000 other than those set out above," the commission said Wednesday.
Banks is a director of BFTCL, which was not registered as a permitted participant in the EU referendum.
Five registered campaigners -- Grassroots Out Limited; Trade Unionists Against the EU; Veterans for Britain; WAGTV Limited; UK Independence Party -- reported donations from BFTCL during the referendum campaign period, totalling £2.4 million ($3.2 million, 2.7 million euros).
Businessman Banks brushed off the probe, tweeting the message "Gosh I'm terrified".
In a statement, he added: "This is the Remain establishment once again trying to discredit the result and it's all starting to get rather boring!"
The pro-Brexit group Leave.EU is already under investigation for campaign finance breaches.
The Electoral Commission said that an initial assessment concluded that "there were reasonable grounds to suspect that potential offences under the law may have occurred".
The investigation will focus on whether the group had accepted "impermissible" donations and on whether it had fully completed its spending return.
The Leave.EU campaign group was founded by Banks in July 2015 and was initially backed by former UK Independence Party (UKIP) leader Nigel Farage but lost out on official campaign status to the Vote Leave group.
By James Pheby