Okay, so I was skeptical that he had ever said such a thing, but it turns out that a magazine called the New York Enquirer (later, the National Enquirer), which was later charged with sedition for opposing america's entrance into WWII did publish an article claiming that he said it.
Churchill claimed that he had said no such thing, and was sued for libel over it: https://www.winstonchurchill.org/publications/finest-hour/fi...
After the publisher was indicted for sedition, the judge dismissed the case.
It sounds to me absolutely nothing like something he would have said.