Boris Johnson has accused a charity set up in the name of Winston Churchill of trying to "airbrush" the wartime leader's "giant achievements".
The Winston Churchill Memorial Trust has renamed itself The Churchill Fellowship and taken down some images of the man voted the greatest Briton in a 2002 BBC poll.
In a statement published on its website, the charity says that "many" of Churchill's views on race are "widely seen as unacceptable today, a view that we share".
But volunteers have accused the organisation of succumbing to a "woke" agenda.
The prime minister is a big admirer of Churchill and wrote a book about him - The Churchill Factor. It is subtitled: "How one man made history."
"The prime minister believes that Winston Churchill was a hero who helped save this country and the whole of Europe from a fascist and a racist tyranny by leading the defeat of Nazism," Mr Johnson's official spokesman said.
"It is completely absurd, misguided and wrong to airbrush his giant achievements and service to this country. The trust should think again."
The charity was developed with Churchill's approval in the last years of his life and awards grants for Britons to pursue social and community causes.
A lengthy tribute and biography have been removed from its website and instead the "Our Story" section briefly mentions his wartime role in defeating the Nazis, while acknowledging "controversy about aspects" of his life.
Regarding race, it says: "We acknowledge the many issues and complexities involved on all sides, but do not accept racism of any kind."
Some of its own volunteers have reportedly accused it of "rewriting history".
"It beggars belief that the man who saved this nation in our darkest hour finds himself cancelled in this way," a source told The Sun.
Another volunteer said the organisation was "bandwagon-jumping" by saying Churchill was racist and accused its chief executive of launching a "woke attack instead of celebrating his life and achievements".
Churchill's statue in London's Parliament Square was defaced several times last year during Black Lives Matter and Extinction Rebellion protests.
The plinth beneath the figure was daubed with "is a racist" and in June had to be boarded up for protection.
In a website statement on Thursday, the charity said it wanted to "set the record straight" and featured a quote in support from Churchill's grandson, Sir Nicholas Soames.
It also once again displayed a picture of Churchill.
The charity said it was "proud of his contribution" in fighting fascism "and of our connection to him" but also reiterated its anti-racism message.
The name change was not to "disown" Churchill, it added, but because the old name "was confusing to people and did not explain what we do".
It said: "Today there is international admiration for Sir Winston's wartime leadership in saving Britain and the world from Nazism.
"There is also controversy about his views on race. We acknowledge the many issues and complexities involved on all sides... None of this takes away from Sir Winston's enormous contribution to the world as we know it today."