Donald Trump deserves "respect" for making it through the Republican primary process, David Cameron has insisted.
But the prime minister said he stood by his view that the wannabe American president was "wrong" in calling for Muslims to be banned from entering the US.
Trump is expected to face Democrat Hillary Clinton in the November election, after fellow Republican Ted Cruz dropped out of the presidential race on Wednesday.
At a joint press conference in Downing Street with Japanese premier Shinzo Abe on Thursday, Cameron said: "It is a matter for voters in the United States to decide who they choose as their next president.
"I have to say that knowing the gruelling nature of the primaries, and what you have to go through, anyone who makes it through that extraordinary contest to lead their party into a general election certainly deserves our respect.
"What I said about Muslims, I won't change that view, I don't change that view. I am very clear that the policy idea that was put forward was wrong, is wrong, and will remain wrong, so I am very clear about that."
Cameron's language about the billionaire Trump was notably more cordial than the words he used in the House of Commons in December. He said then: "I think his remarks are divisive, stupid, and wrong. If he came to visit our country, I think he would unite us all against him."
George Papadopolous, an adviser to Trump, has demanded an "apology or some sort of retraction" from Cameron for these comments.