Prices for frozen vegetables are already on the rise in UK supermarkets, with growers and processors alike pointing the finger at the summer heatwave.

It is the first evidence of the impact of this year's damaged vegetable crops, which suffered in both quality and quantity from the drought.

Branded peas were the first to feel the heat, with a 1lb (454g) pack from Birds Eye rising 13p to 89p in Tesco - a 17% increase.

It follows a warning from leading supermarket own label pea packer Christian Salvesen that the UK was facing a 20% shortfall. MD Colin Miles said there would be 20 million fewer bags of peas in supermarket freezers this year. The company said it was still in post-harvest price negotiations with retailers, but predicted rises across the board.

Martin Riggall, chief executive of the Processed Vegetable Growers' Association, said: "The industry has been squeezed beyond the limit, and the pea crop is so marginal, even in a good year, that when there is a bad year almost everybody in the chain will lose money - that's the reason for pushing up prices.

"But all the evidence we have points to consumption of frozen peas being unrelated to price. Consumers don't buy more if they are on offer because they have limited freezer space, and if the price goes up there is no danger of them switching to another frozen veg."

In spite of recent rain, the outlook remains poor for crops such as cauliflower, broccoli and sprouts, which will be harvested this autumn and winter, says NFU horticulture board chairman Richard Hirst. "The damage to some plants has already been done."

Data from The Grocer 33 shows that prices are already 11p higher than last August for a 2lb bag of supermarket own label peas at 96p. At Tesco, 1kg of garden peas is up 26p to £1.05.

European processors' group OEITFL says raw material prices across Europe are rising, forcing renegotiations with retailers.