Crop production in Britain could plummet if climate change affects an ocean current which brings warmth to the UK, scientists have warned.
Land suitable for arable farming could plunge by a quarter, reducing crop value by £346 million a year.
It will happen if an ocean current known as Atlantic Meridional Overturning Circulation (AMOC) hits a ‘tipping point’.
AMOC brings heat from the tropics, making Britain warmer and wetter than it would otherwise be - but it has weakened by an estimated 15 per cent over the last 50 years.
The collapse could leave Britain 3.5C cooler and unable to grow many crops, the study says.
The main problem would be reduced rainfall and, though irrigation could be used to compensate, the researchers said the amount of water and the costs would be too high.
Dr Paul Ritchie, of Exeter University, said: "If the AMOC collapsed, we would expect to see much more dramatic change than is currently expected due to climate change.
"Such a collapse would reverse the effects of warming in Britain, creating an average temperature drop of 3.4C and leading to a substantial reduction in rainfall of 123mm during the growing season.
"These changes, especially the drying, could make most land unsuitable for arable farming."
Scientists said the AMOC is one reason that average temperatures in Britain are warmer than those of many places at similar latitudes.
For example, Moscow and the southern extremes of Alaska are both further south than Edinburgh.
The study, published in the Nature Food journal, examines a "fast and early" collapse of the all-important current pattern.
Professor Tim Lenton, Exeter University's Global Systems Institute lead, said worst-case scenarios must be considered when calculating risks.
He added: "Any risk assessment needs to get a handle on the large impacts if such a tipping point is reached, even if it is a low-probability event.
"The point of this detailed study was to discover how stark the impacts of AMOC collapse could be."
The study follows a recent paper by the professor and his colleagues warning of a possible "cascade" of inter-related tipping points.
Professor Lenton said the new study reinforces the message that we would be "wise" to act now to minimise the risk of passing climate tipping points.
Growing crops is generally more profitable than using land as pasture for livestock rearing, but much of northern and western Britain is unsuitable for arable farming.
Professor Ian Bateman added: "With the land area suitable for arable farming expected to drop from 32 per cent to 7 per cent under AMOC collapse, we could see a major reduction in the value of agricultural output.
"In this scenario, we estimate a decrease of £346 million per year - a reduction of over 10 per cent in the net value of British farming."