Wealthy Brexit backer Arron Banks (pictured) may have been involved in smuggling diamonds out of South Africa, it has been alleged

Wealthy Brexit backer Arron Banks may have been involved in smuggling diamonds out of South Africa, it has been alleged.

Britain's National Crime Agency has been passed claims that Mr Banks, who owns diamond mines in South Africa, tried to get hold of black-market diamonds from Zimbabwe.

It is alleged that he was trying to supplement his South African diamond exports with the illegal supply from Zimbabwe, pretending they were all from his mines.

The allegations by Mr Banks's former business partner also include the claim that he was 'dealing with Russians' in the diamond scheme, The Sunday Times reported.

Mr Banks has denied the claims, calling them 'ludicrous' and a 'concoction of nonsense'.

The multi-millionaire donated millions to Ukip before the EU referendum and in 2016 backed Nigel Farage's Leave.EU group with an £8million donation.

He has since faced scrutiny about the Brexit campaign's alleged links to Russian money.

Mr Banks, one of the self-described Bad Boys of Brexit, is already under investigation by the NCA over his donation to Leave.EU three years ago.

The Electoral Commission had referred the case after investigating whether Mr Banks was the 'true source' of the funding.

The multi-millionaire donated millions to Ukip before the EU referendum and in 2016 backed Nigel Farage's Leave.EU group with an £8million donation (he is seen with Mr Farage in 2014)

Mr Banks, 52, made his fortune from the Bristol-based insurance broker Brightside which he founded.

He then went on to found another firm, GoSkippy, and is now said to be worth £100million.

He is married to Russian Ekaterina Paderina and has five children.

Originally a modest Tory donor, in 2014 he defected to Ukip in anger at then-PM David Cameron's stance on Europe.

He was pictured alongside Donald Trump when the President met Nigel Farage in New York just days after his shock US election victory.

Last year Mr Banks claimed he had rejoined the Conservative party along with his associate Andy Wigmore but the Tories said their applications had been rejected.

In May 2018 Leave.EU was handed a fine of £70,000 for breaching finance rules in the 2016 referendum.

After failing to become the lead campaign group for the pro-Brexit movement, it had a spending limit of £700,000 but the Electoral Commission found it exceeded that cap.

Earlier this year the European Parliament said it would investigate claims that Mr Banks had donated £450,000 to Mr Farage after the referendum.

MailOnline approached Mr Banks for a comment but he is yet to respond.