Left-wing "Winterval"?

I've been reading The Winterval Myth, and wondering, what's the left-wing equivalent? What's a story that

• is told over and over
• to support a left-wing narrative
• as if it were an unquestioned fact, a simple matter of public record
• when it is in fact incontrovertably false
• and has been utterly debunked in detail?

Obviously I tend to think that those I've got more sympathy for have a more fact-based way of talking, but it would be odd if there were no examples. There must be some program that a specific named Tory council implemented, only they never did, or some awful thing that Thatcher or Cameron never in fact said (or whose meaning is so utterly changed by the context that once you knew the context you couldn't possibly apply the original meaning to it) or some terrible "fact" about nuclear power that isn't a fact at all. Anyone able to link me up?

Thanks!