The Tories have accepted another £5 million from the donor who said Diane Abbott made him “want to hate all black women” and “should be shot”.
Frank Hester gave the party £10m last year, making him the Conservatives’ biggest donor.
According to Tortoise, the health company executive has donated a further £5m so far this year, although it is yet to be declared to the Electoral Commission.
The revelation has led to fresh calls for Rishi Sunak - who has said Hester’s comments were “racist and wrong” - to hand the money back.
Labour leader Keir Starmer said: “It makes the situation worse, because it begins to give an explanation as to why Rishi Sunak will not hand this money back.
“This is a significant contribution to their electoral campaign. And he won’t hand it back. Now this is the same prime minister who took it on himself to do a broadcast, essentially walking into our living rooms two weeks ago Friday, at ten to six, to parade as a unifier and a man that could bring people together.
“Amongst the comments, not just racist and misogynistic about Diane Abbott, this is a donor who said she should be shot. There’s only one answer to returning that money. It’s a test for Rishi Sunak. He’s failing that test.
“And if this report is true, I think it raises serious questions about what his real motivation is in clinging on to that money in the current environment.”
Liberal Democrat chief whip Wendy Chamberlain questioned whether the Tories’ initial decision to defend Hester was linked to the extra cash.
She said: “The Conservative Party must urgently confirm whether these reports are true and if so hand this tainted money back.
“The Conservative Party has dragged its feet in condemning these racist remarks for what they are. If that was in any way linked to this £5 million donation it would show this scandal is even worse than we thought.
“People like Hester and his attitudes need to be nowhere near our politics. Conservative politicians need to learn that just because someone gives you millions of pounds that does not make the inexcusable, excusable.”
Post office minister Kevin Hollinrake said yesterday that he would be happy for the Tories to accept another £10m from Hester because “we don’t believe Mr Hester is a racist”.
A Conservative spokesperson said: “Declarable donations will be published by the electoral commission in the usual way.”