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.