Harborne has already donated millions to Reform and Farage, who is currently under investigation by the parliamentary standards commissioner over whether he should have declared a £5m cash gift from Harborne ahead of the 2024 election.
Farage has argued that he was under no obligation to register the “purely private” gift, as it was unrelated to his parliamentary or political activities.
The party is also facing scrutiny after a broadcast by Channel 4 News last week showed two senior Reform aides apparently suggesting a way around electoral law to secure foreign party donations.
The Metropolitan Police has said it is investigating, while the party denies any wrongdoing.
The force is also looking into donations given to the party by Fiona Cottrell, mother of longstanding Farage ally George Cottrell, as well as a company controlled by Tice.
Harborne wrote on Saturday that he had “already accumulated enough wealth for the rest of my life”, while Reform was a “start-up party” that lacked “the benefit of hundreds of years of patronage”.
“A start-up party needs more money than can be provided by membership fees alone, to build and sustain itself and be ready for government,” he said.
Harborne and Delo’s donations mark the largest sums received by a UK political party since they had to begin declaring them in 2001.
Delo, who also announced his donation in a Telegraph op-ed, said he was giving the money away because he wanted a “fair fight and a level playing field”. He said in April he was moving back to Britain from Hong Kong.
Addressing the recent scrutiny of Reform’s finances, he said: “My conclusion from Reform’s recent troubles is that they should spend less time trying to raise funds to compete on equal terms and more time preparing for government.”
Last year, he was given an unconditional pardon by US President Donald Trump over a breach of anti-money laundering laws at his crypto trading platform, BitMEX, to which he had pleaded guilty in 2022.
There are currently no restrictions on the amount of money UK-based donors can give to political parties.
However, the Labour government has introduced a £100,000 cap on donations from British citizens living overseas, and plans to introduce a similar one for those who have recently returned to the UK.
There were nine donations of £1m or more to political parties in 2025. The largest was £9m given to Reform UK by Harborne.
Labour had five donations of £1m or more – totalling nearly £10m – and the Conservatives had three of £1m each.
Labour said Reform and Farage still had “serious questions” to answer about their finances.
Party chairwoman Bridget Phillipson said Reform were “drowning” in “sleaze and scandal”.
She added: “It’s time Farage and Reform came clean with the public, fully co-operated with the ongoing police investigations and prove they’re not just in it for themselves.”
Rachel Millward, deputy leader of the Green Party, told BBC News it wanted a cap on donations from individuals of £500,000.
She said the donations to Reform were “absolutely staggering amounts”, adding: “What I am very frustrated about is the influence of extreme wealth and the super rich. What I want to see is people in politics representing the needs of their communities and ordinary people.”
Liberal Democrat Cabinet Office spokeswoman Lisa Smart called for the government to introduce emergency legislation to cap donations.
She said: “These are eye-watering amounts of money. This is real emergency for our democracy. It presents a very clear and present threat.”
Labour MP Stella Creasy and other backbenchers had proposed an amendment to the Government’s Representation of the People Bill that would stop donors giving parties over £100,000 a year.
But the amendment was never debated in the Commons after the government said it would set up a task force to investigate the issue. The bill will be debated in the House of Lords on Monday.
Duncan Hames, Director of Policy and Programmes at campaigning charity Transparency International UK, said: “This is a watershed moment, with two billionaires pledging £72m to one political party in less than 48 hours.
“This situation is now completely out of control, and makes an irrefutable case for government to bring forward an annual cap on political donations, and fast.”