Two poor potato seasons in succession are threatening to create a national shortage of home-grown spuds.

New estimates for the size of this year's crop have put volumes slightly below last year at 5.45 million tonnes - 18% off highs of five years ago.

Stocks have also been hit by last year's drought pushing prices 12.5% higher than they were in November 2006.

"Last year in the key growing period of June and July it was too hot and this year it was too wet " said Neil Beeton, sales director for potato supplier MBM Produce, which markets the Potato Lovers brand.

"Wastage levels are likely to be double usual levels due mainly to greening, growth cracks and misshapen potatoes that need to be removed.

"It's creating a national availability problem, and the area most likely to be affected is retail, where demand is highest for good appearance and shape."

Yield per hectare is nearly 10% lower than the five-year average, and the market is responding by raising prices.

British Potato Council figures show a current average price of £136/tonne compared with £119/tonne for the same week last year.

If the current high prices for premium potatoes continued, imports would inevitably rise, said market information manager Rob Burrow.

"Exporters may start looking at the price differential between us and the Continent and traders will try to take advantage," he said.

"If imports come in, they may put a ceiling in the market, keeping prices from rising further.

"It would make the market more stable but may not provide growers with expected returns."

Burrow also said there were signs that potato production was shifting to northern and eastern parts of the country in response to the extreme conditions of the past two seasons.