Out of 294 samples DNA-tested by the Food Standards Agency, 33% were wrongly labelled while 17% were not the variety they claimed to be.
The samples were taken from a wide range of retailers, from smaller fruit and vegetable stores up to the major supermarket chains.
Potatoes on retail sale are required by law to be labelled with the name of the particular variety.
Rosemary Hignett, head of labelling and standards at the FSA, said: “It is clear consumers are not always getting what they are paying for and this is unacceptable.”
She said retailers were increasingly marketing the differences between varieties, with price variations up to 40%.
She said there was a particular problem at wholesale markets.
The potatoes most likely to be mislabelled were King Edwards, with 16 out of 37 samples incorrect.