The British chip has been left an inch shorter by the 2018 heatwave, according to a report on the risks to UK fruit and vegetable growing from climate change.
Future yields of fruit and vegetables grown in the UK, from the humble spud to grapes producing British wine, could be hit by extremes such as longer-lasting and more intense heatwaves, downpours and flooding.
A report from the Climate Coalition of environmental and social groups said last year’s heatwave and drought saw yields of potatoes fall 20% compared to the previous season.
The summer’s extreme weather - which the Met Office said was made 30 times more likely by climate change - also hit carrots and onions.
As well as a drop in potato yields, farmers had problems with smaller and misshapen spuds – leaving the average British chip more than an inch smaller, the report said.
It is not just drought causing problems as more than half of farmers in the UK say they have been affected by severe flooding or storms in the past decade, with climate change set to bring more record-breaking rainfall.
Some English vineyards reported up to three-quarters of their crop being damaged by the late spring frosts in 2017.
Shoppers could find British-grown potatoes and other fruit and vegetables harder to come by in the future as a result of the changing climate, the report warned.
Climate Coalition director Clara Goldsmith said: "Losing an inch off our chips is no laughing matter.
"Even worse if we lose supplies of our much-loved British spuds altogether.
"We should be doing all we can to help safeguard our homegrown fruit and vegetables for future generations."
By the 2050s, climate projections suggest the amount of land is currently well-suited for potatoes could decline by three-quarters, the report said.
The report is part of Climate Coalition’s "show the love" campaign which celebrates things that could be lost if global warming is not tackled.
The coalition, made up of 130 organisations ranging from WWF, the Women’s Institute, RSPB and National Trust, to aid agencies such as Christian Aid and Cafod, is calling for cuts to the emissions driving up temperatures.
Gareth Redmond-King, from WWF, said: "It should be unthinkable to us that the humble spud, a much-loved staple of the British diet, could become a delicacy.
"To be able to enjoy our mash, chips or jackets for years to come, we need to take measures to tackle climate change urgently."
Action is needed to cut emissions from food production and retail, and by reducing food waste, buying local and seasonal foods and shifting diets towards more fruit and vegetables, the report said.
Polling for Climate Coalition found three-quarters of consumers said they would be willing to buy more misshapen fruit and vegetables, 62% would buy more locally-sourced food and 57% would opt for more seasonal produce.
Environment Secretary Michael Gove said: "High-quality, locally-grown fruit and veg are a crucial component of British diets.
"Yet, as we saw with last year’s drought, this nutritious food, and the livelihoods of the hard-working farmers who grow it, are increasingly threatened by more extreme weather and increased pests and diseases as a result of climate change.
"We will use powers in the Agriculture Bill to reward farmers who reduce their emissions and adapt to the effects of climate change through our new environmental land management scheme."