Arron Banks, Ukip's biggest donor and one of the first Britons to meet Donald Trump after his election victory, has denied claims he offered a “bribe” to a major UK political party in exchange for support for his Leave.EU Brexit campaign.

The allegation was made by senior figures in the Northern Irish Democratic Unionist Party, who said Mr Banks offered them a financial sum, thought to amount to six figures, if they chose to back the Ukip dominated Leave.EU campaign, instead of its rival Vote Leave.

At the time of the alleged offer, both Brexit organisations were competing to be selected as the official campaign group that would receive formal public funding for the referendum battle. A spokesperson for DUP, which eventually backed Vote Leave, told The Independent: “Mr Banks offered the party financial support if it changed which bidder it backed. The party neither accepted money from Arron Banks nor changed his mind.”

But millionaire businessman Mr Banks, who was part of the Ukip delegation invited to meet Mr Trump in New York last month, insists the offer was the other way around. He says the DUP asked him for money in exchange for backing the Leave.EU campaign.

The Independent understands the allegations relate to a meeting on 12 February in London, at private members club 5 Hertford Street, where a senior member of the DUP met Mr Banks.

Donald Trump and Arron Banks (Twitter/Leave EU)

At the time Vote Leave and Leave.EU were lobbying against each other to secure the £600,000 of public funding available for the official anti-EU campaign. Support from the DUP was perceived to be a prize catch for both camps for that race, because it had eight MPs and was the largest party in Parliament to support leaving the EU.

Details about the negotiations were first aired in Mr Banks’ memoirs, The Bad Boys of Brexit, when he wrote: “The DUP is demanding cold, hard cash in exchange for its support! Thirty grand a month, to be precise. I know Northern Irish politics is dirty, but this is crazy. It all came about because Farage is mates with [DUP MP] Ian Paisley Junior.”

A spokesperson for Mr Banks told The Independent he stands by his account in his memoir and rejects any suggestion he offered the DUP money. The DUP gave their backing to the Vote Leave campaign, which was later selected as the official Leave campaign.

During the referendum, it caused controversy after buying a four page advertisement supporting Brexit in the Metro newspaper, which is not distributed in Northern Ireland. At the time, the party denied questions of whether the move was an attempt to circumvent spending limits in the campaign, saying they were merely joining a national debate which involves all regions of the UK.