Brexit bankroller Arron Banks is being investigated by South African police over claims of corruption, fraud, diamond smuggling and firearms offences, The Mail on Sunday can reveal.

The British businessman, who pumped £9 million into the Leave.EU campaign, had a criminal case opened against him earlier this month by an elite crime unit known as The Hawks.

Prosecutors in South Africa were last night poring over a dossier of allegations about Banks and diamond mines he owns in the state of Lesotho.

Brexit bankroller Arron Banks, pictured with his wife Catya Banks, is being investigated by South African police. He had a criminal case opened against him earlier this month by an elite crime unit known as The Hawks

The UK’s Serious Fraud Office is understood to have been handed the same evidence as the South African authorities, but last night refused to say whether it had opened its own probe.

It comes as multi-millionaire Banks faces increasing pressure over allegations that he was backed by Russia to influence the outcome of the EU referendum.

The criminal probe in South Africa was confirmed by Brigadier Hangwani Mulaudzi, spokesman for The Hawks. He said: ‘We are investigating a number of allegations.’

Banks last month admitted paying thousands of pounds to a government minister in Lesotho, but insisted it was not a bribe.

Arron Banks (pictured second from the left) with Donald Trump, smiling next to Brexiteer Nigel Farage

The South African authorities are probing several allegations, including that Banks paid off corrupt government figures in order to obtain a mining licence.

He is also claimed to have imported diamonds and planted them at his mines to dupe investors into thinking the ventures were more profitable than they actually were.

The Brexiteer is alleged to have sought financial backing for diamond mines from Russia.

It is claimed he used the money from investors to fund his Leave.EU campaign.

And Banks faces claims that he illegally smuggled a £30,000 uncut diamond out of Africa, and that he bought weapons without a firearms licence.

The criminal probe was launched after police were handed a dossier of evidence by a Johannesburg-based fraud investigator.

Banks denied wrongdoing and said the allegations stemmed from claims made by Chris Kimber, a disgruntled ex-business partner.

This month it emerged Russia’s ambassador in London offered Banks a slice of a £6 billion deal to invest in state-controlled gold mines ahead of the Brexit poll.