People are unknowingly buying fakes from Chinese firms through online marketplaces, reports suggest.
Reports suggest a rise in complaints that stamps bought from legitimate stores are being deemed counterfeit. Anyone who receives a letter with a fake stamp is charged £5 by Royal Mail.
Conservative MP Iain Duncan Smith told BBC Breakfast: "China is behind it."
A Royal Mail spokesman said: "We are working hard to remove counterfeit stamps from circulation."
Consumers are being warned to look out for strange perforations around the edge of a stamp, a shine to the surface or the colour looking off.
Because people would lose attention if they tried to use a phrase longer than "China", and most people on this side of the world wouldn't know or retain a specific placename in China unless they had specific interest in the country.
The news could throw something like "Malingshu province" and most people wouldn't bat an eye.
... despite the fact that that province name is fake and is in fact a mangled transliteration of one of the Mandarin words for "potato".
Honestly I am learning Chinese and those kind of bizarre mnemonic devices are the only thing that gets it to stick in your head. Horse with bell on neck eating a potato. I will think of that and remember the word, or at least be part of the way there!