David Cameron has admitted he owes an apology to former Conservative party treasurer Peter Cruddas, who was ostracised from the party following newspaper sleaze allegations.
Mr Cruddas was dismissed from his role after the Sunday Times reported in March 2012 that he was charging potential donors £250,000 to meet the Prime Minister but has since won a libel action from the newspaper.
In the wake of the original newspaper report Mr Cameron gave a speech condemning Mr Cruddas's alleged actions as "completely unacceptable and wrong".
High Court judge Mr Justice Tugendhat criticised the Mr Cameron's response, saying he had subjected his former colleague to a "massive public humiliation".
"The Prime Minister did not know what Mr Cruddas had said. All he knew was what the Sunday Times had reported," said the judge in his finding.
Mr Cameron said he was "very sorry" about the treatment of Mr Cruddas, who claimed he was "cut off" by the party and "made to feel like an outcast" by the Prime Minister.
"I rather think I do owe him an apology," he admitted. "Had I known at the time how badly the journalists had behaved, I might have been in the position to take a different approach.
"I am very sorry about that. I congratulate Peter Cruddas on his victory and on the verdict he has won. I think it is very deserved.
"He has done a huge amount for this country. I look forward to meeting him after the summer."
Mr Cruddas, who was also awarded £500,000 in legal costs, said his "good name had been restored".
Speaking after the High Court ruling last week Mr Cruddas said, "My world was turned upside-down when that article was published. I remember vividly having to walk into my offices the day after the article was published and face 500 of my staff, many of whom had a clip of the Sunday Times interview on their video screens. It was humiliating.
"I was also embarrassed to accept invites to events which meant that my charities suffered. The Conservative Party cut me off within two hours of the story breaking and did not want to hear my side of the story.
"I was constructively dismissed from my role as party treasurer and made to feel like an outcast as the Prime Minister and the party lined up to criticise me on television and radio. This hurt me immensely and further damaged my reputation."
Mr Cruddas, who prior to becoming treasurer was one of the party's biggest donors, also succeeded in his claim for malicious falsehood against the weekly newspaper.
Following Mr Cameron's apology Labour MP Steve McCabe said: "If David Cameron thinks he owes Peter Cruddas an apology, perhaps he should invite him round to one of his famous dinners for donors in Downing Street to tell him to his face.
"Meanwhile, six weeks after David Cameron promised to publish the results of Lord Gold's internal inquiry into Tory Party donations, we're still waiting. It's time he got on with it."
The Sunday Times intends to appeal the High Court decision.