Fans of big name foodstuffs like Heinz Ketchup, HP Sauce or Colmans mustard are generally sure they’d spot the difference if you forced them to try a store’s own-brand alternative.

But one mischievous hubby put that to the test for a whole year – and got away with it.

The prankster owned up to his deception on Reddit, sharing a photo of himself “piping the Aldi mayo into the same Hellman’s bottle we’ve had for a year so the Mrs will not know she’s a commoner”.

Not only was the substitute mayo Aldi’s cheaper version, it was full-fat too. The cheeky chap’s wife was insistent on keeping Hellmanns’s low-calorie offering in her fridge.

Sooner or later his wife's going to wonder about the miracle of the everlasting mayo jar

"Full fat into a lighter bottle. Devious," said one user.

So if our hero's wife has gained a pound or two over the past 12 months, she knows who to blame now.

One commenter on the original story fumed: “If someone swapped lighter mayo for full-fat mayo I would be livid. All the extra calories I'd consume without knowing it…”

The other question, of course, is when she’s going to notice that they’ve had the same “magic” squeezy bottle of mayonnaise for a whole year without having to replace it.

As someone pointed out on Reddit: “Has she not peeked the expiry date?”

More than 1,000 people have so far up-voted the frankly devious post with dozens commenting on it.