Reform’s fundraising has been under scrutiny with police announcing an investigation over allegations it broke foreign funding laws, following a broadcast by Channel 4 News last week.
The party denied any wrongdoing and said it would co-operate with the investigation.
Farage is also under investigation by the parliamentary standards commissioner over whether he should have declared a £5m cash gift he received from Thailand-based cryptocurrency investor Christopher Harborne ahead of the 2024 election upon his election as an MP.
Farage argues he was under no obligation to register the “purely private” gift, as it was unrelated to his parliamentary or political activities.
The Metropolitan Police is also investigating whether payments to Reform in the weeks before the last election complied with donation laws.
The police inquiry is looking at donations given directly to the party by Fiona Cottrell, mother of longstanding Farage ally George Cottrell.
It is also examining payments from a company controlled by Reform’s deputy leader, Richard Tice, which received £1m from Fiona Cottrell in June 2024.
The restrictions on donations from Britons living abroad prompted a furious row with Reform and its key donors, who have accused Labour of trying to stymie their party’s progress.
The government has also sought to prevent overseas voters moving to the UK from giving more than £100,000 for a year after their arrival as part of the Representation of the People Bill, which has its second reading in the Lords on Monday.
Last year Harborne gave a single donation of £9m to Reform – which was the biggest single donation to a UK political party by a living person at the time.
The Conservatives had received £10m as a legacy but that too has been eclipsed by Delo’s latest donation.
Responding to the donation, a Labour Party spokesperson said Farage was “still up to his neck in scandal” and “the questions he faces aren’t going away – in fact they’re piling up”.
“Reform UK can’t buy their way out of questions about sleaze, criminal mates and dodgy finances,” they said. “It’s time Farage and Reform finally came clean with the public, co-operated fully with the police, and proved they’re not just in it for themselves.”
Liberal Democrat Cabinet Office spokesperson Lisa Smart said Farage wanted to “bring Trump’s America to our shores by buying his way into power”.
“He’s trying to get into Number 10 as if it’s a stop on a monopoly board,” the Liberal Democrat added. “It can’t go on like this. Andy Burnham needs to introduce a cap on political donations. Our democracy depends on it.”