Reform has said it will use the money to fund its preparations for office.
Peers are to debate calls for a cap on political donations amid concern from campaigners over two £36 million donations from crypto-billionaires to Reform UK.
The donations from Christopher Harborne and Ben Delo, disclosed over the weekend, together amount to three quarters of the money spent at the last general election by all parties combined.
Reform has said it will use the money to fund its preparations for office, and that the men want “nothing” in return.
But campaigners have said the £72 million gifts demonstrate the need for a cap on political donations, and Spotlight on Corruption said the situation “creates risks that the game will be rigged in favour of those with the most cash”.
Proposals for a cap are likely to feature heavily in the House of Lords, which will debate the Government’s Representation of the People Bill on Monday.
The Bill already contains measures limiting donations from overseas electors to £100,000 a year, but attempts by MPs to impose a general cap failed after the Government promised to task officials with investigating how a measure would work.
On Sunday, Communities Secretary Angela Rayner suggested a cap was still on the table, telling the BBC she wanted to stop people “being able to overpower and buy their way into democracy”.
The Liberal Democrats are likely to push for a cap, having called for “emergency legislation” to impose one and saying the donations exposed “a dangerous flaw in our democratic system”.
Sharon Graham, general secretary of Unite, has suggested donations from trade unions should be exempt from any cap, saying were “not the same as two crypto millionaires waking up and giving £72 million”.
Meanwhile, questions remain over whether Reform will be able to keep all of the £72 million.
Robert Jenrick, the party’s economic spokesman, said on Sunday the donations were “entirely in line with the law as it is, and as far as we know, the law as it’s going to be in the future”.
But Ms Rayner appeared to suggest they could be covered by the cap on overseas donors, which will be backdated to March 25.
The rules, which limit donations from overseas electors to £100,000 per year, were proposed in a review by former civil servant Philip Rycroft aimed at countering foreign influence in UK politics.
They also apply to donations made in the first year that someone moves back to the UK.
Mr Delo has been based in Hong Kong but said in April he would return to the UK to avoid restrictions on overseas donors, and Mr Harborne is based in Thailand.
Ms Rayner told the BBC: “With the retrospective action, anyone that’s received donations that don’t comply with what was in the Rycroft review, what legislation is currently going through Parliament, would have 60 days to return that money.
“That is not for those individuals, let me be really clear, I do not understand those individual circumstances, but that the retrospective action will apply from March 25.”
