A dry summer has shrunk the British potato crop and raised a daunting prospect for Britons: a shortage of chips. Fish and chip shops say they will have to reduce portion sizes and raise prices for the national dish. Potato prices have already doubled this year and could go even higher, said the National Federation of Fish Friers, which speaks for the country’s 10,500 chip shops.

Andrew Crook, the NFFF president, said: “We have to cover our costs. Prices will go up and many will reduce the size of a portion. A lot of small shops will probably sell up.” A 25kg sack of potatoes, enough for about 40 portions of chips, costs £12, up from £6 last year, and Mr Crook forecasts it will soon be £20. Fish prices have also doubled since 2011, he added. Mr Crook’s shop near Chorley in Lancashire charges £4.20 for cod and £1.90 for a portion of chips and has already increased prices for each by 10p this year.

Fish and chips is thought to be the UK’s most popular takeaway choice by volume, with 380m portions served a year, according to the NFFF. The price pressure could have unintended benefits. Mr Crook has long pushed for a cut in portion sizes. “McDonald’s will give you 5oz, we are serving 12, 14 or 16oz.” The industry has recommended a standard size of 10oz while the Food Standards Agency said anything above 8oz is unhealthy.