It’s been called “the grate cheese robbery.”

But it’s no joke to the tight-knit world of artisanal British cheese makers, which is reeling from the disappearance of 22 metric tons of rare Cheddar worth at least 300,000 pounds, about $390,000, in what appears to be the biggest con to hit their industry in decades.

“We never imagined that this sort of thing would happen,” said Patrick Holden, whose dairy farm in Wales made some of the missing Cheddar.

“Of course,” he added, “people have bad debts. But theft? I mean, that just doesn’t happen.”

It all started in July. That’s when Neal’s Yard Dairy, a leading London cheese retailer, said that it had received a major order from what appeared to be a “legitimate wholesale distributor for a major French retailer.”

The company turned to Mr. Holden’s dairy farm and to two other cheese producers — Westcombe Dairy and Trethowan Brothers — to fill the order, which, at 22 metric tons, was more than one could provide alone.

Mr. Holden said that he was initially flattered. A French chain wanted to buy that much British cheese? And Cheddar, such a quintessentially British variety?

“We’d been going around, proudly, saying: ‘Guess what, a French supermarket is buying our cheese,’” Mr. Holden said, chuckling.