Brexit campaigner Arron Banks has mocked investigators who are looking into whether his multi-million-pound donations during the 2016 EU referendum breached campaign finance rules.
Mr Banks, the former Ukip donor and Leave.EU chairman, tweeted "gosh I'm terrified" after the elections watchdog probe into donations and loans was announced.
The Electoral Commission will also examine Better for the Country Limited (BFTCL).
The company, which was not registered as a permitted participant in the referendum, lists Mr Banks as a director and has its registered office at the same address at Leave.EU.
Five registered campaigners reported donations from BFTCL totalling more than £2.3 million.
Mr Banks also made three loans worth £6 million on non-commercial terms to Leave.EU.
Among the areas the Electoral Commission will look at include:
Whether BFTCL, Mr Banks and recipients of funds from them may have committed offences under election law.
Whether BFTCL was the true source of donations made to referendum campaigners in its name, or if it was acting as an agent
What steps the recipients of the donations took to verify the identity and permissibility of BFTCL as a donor
Whether Mr Banks was the true source of loans reported by a referendum campaigner in his name
Bob Posner, the commission's director of political finance and regulation, and legal counsel, said: "Interest in the funding of the EU referendum campaigns remains widespread.
"Questions over the legitimacy of funding provided to campaigners at the referendum risks causing harm to voters' confidence.
"It is therefore in the public interest that the Electoral Commission seeks to ascertain whether or not impermissible donations were given to referendum campaigners and if any other related offences have taken place."