Visiting my grandparents recently, I was struck by a phrase my grandmother said frequently: “go tell that to your Dutch uncle”.

I’d never heard this before, and neither my grandfather or mother use the phrase or could tell me where it was from. A quick search doesn’t reveal anything of its origins. My grandmother used it jokingly when she thought someone was saying something fanciful or that she didn’t believe. I got the impression that the “Dutch uncle” was someone fictional, who would believe the stories you would tell.

A “Dutch uncle” is referenced here as “a term for a person who issues frank, harsh, and severe comments and criticism to educate, encourage, or admonish someone”, whereas here it is “a person who bluntly and sternly lectures or scolds someone, often with benevolent intent”. Perhaps my grandmother was using it more in the sense that the Dutch uncle was someone who would punish the story-teller for their lies.

My grandmother is in her eighties and from the West Country in England. Perhaps this is a regional idiom?

Can anyone shed any light on this strange phrase?