The countryside is being cut off because the mobile phone network switches off the 3G signal, leading rural organizations warn.
Britain's mobile networks have started shutting down their 3G services - which allow people to use the internet - in preparation for the rollout of 5G.
But data from Ofcom shows that 7 percent of Britain, which is almost entirely rural, does not have access to the 4G and 5G networks that are replacing 3G.
Rural groups say it will leave people living in rural areas isolated and the shutdown will put lives at risk as farmers will be left without location services in the event of an accident.
The networks and the regulator are facing calls to halt the switch-off until 4G coverage is improved to prevent black spots from increasing in rural areas.
"It is important that action is taken to avoid a situation where rural businesses are cut off from 3G without reliable 4G coverage," said Rachel Hallos, vice-president of the NFU.
"In many parts of rural areas, an unreliable mobile signal prevents farmers from running efficient and productive farms.
"It can also leave farmers without communication in times of crisis."
Telegraph analysis of Ofcom data provided by the mobile networks shows that the shutdown will reduce access to data services by up to 11 percent.
The worst affected area is Copeland, in Cumbria, followed by Dwyfor Meirionnydd and Montgomeryshire.
But mobile networks have also admitted that official data is likely to underestimate the lack of connectivity, which they say could be affected by rain, leaves growing on trees or housing extensions.
Official data shows that at current 4G coverage levels, a further 2 percent of the country will end up in a data blackspot if the 3G connection is turned off.
The heads of two prominent rural groups that use Vodafone told The Telegraph that their access to mobile internet had been significantly reduced since their 3G was switched off.
This is despite Ofcom's coverage check suggesting they have good coverage.
Vodafone and EE are the first networks to complete the full 3G switch-off on their networks, with Three starting this month and O2 completing next year.
The four main providers also share 3G services with the smaller networks, including GIFFGaff and Tesco Mobile.
'4G not available in some rural areas'
The timeline for the shutdown was set by the networks, after the government set an original deadline of 2033.
Networks say calling should still be possible over the 2G network, but newer handsets may not be able to access it.
George Eustice, the former Rural Affairs Secretary, said Ofcom should "consider requiring providers to maintain 3G in some rural areas until 4G becomes available".
"Everyone agrees that moving to 4G and 5G would be better for consumers, but we cannot ignore the fact that 4G is simply not available in some rural areas," he said.
A government and industry-funded initiative to boost 4G capacity in rural areas, called the Shared Rural Network, has stalled, with Vodafone, O2 and Three all seeking a two-year extension of the first phase.
Victoria Vyvyan, president of the Country and Land Business Association, said network operators have a responsibility to provide access to ensure communities stay connected.
"Where 4G is not available, 3G must remain, otherwise rural communities will fall victim to the worst form of digital exclusion," she said.
"Entrepreneurs will find it harder to grow their businesses, people will feel more marginalized and it could even put lives at risk, leaving the public with nowhere to go if they are injured in remote areas without emergency services cover."
Martin Lines, head of the Nature Friendly Farming Network, said much of the coverage on his farm in St Neots had disappeared since 3G was switched off, despite being just 15 miles from the center of Cambridge.
"We could get 3G almost everywhere, but one day it just disappeared," he said.
'If my data disappears, I disappear'
Mr Lines uses the internet as a safety tool, ensuring he can inform his family or emergency services of his exact location if he has an accident on his 400-hectare farm.
"If my data disappears, I disappear," he said. "This has put us in a very vulnerable position."
He said it has affected his ability to do business as he cannot access crop reports and weather forecasts, or use hi-tech farming equipment on certain parts of his farm.
Julia Aglionby, a surveyor in Cumbria, said she had noticed "a big difference" since her Vodafone 3G service was switched off.
"There's just not enough reporting," says Dr Aglionby, who has stepped down from her role as head of the Foundation for Common Land as she runs as a potential Lib Dem candidate.
"This is something I hear from people every day," she says.
The lack of internet affected people receiving flood warnings, using chat helplines or doing everyday business.
"There are real financial costs as well as safety concerns," she said. "You just don't have the functionality to do business."
The Local Government Association has previously accused mobile networks of "doing their own homework" and relying on optimistic modeling to provide 4G coverage figures.
A spokesperson for the Department of Science, Innovation and Technology said: "Everyone should have access to a fast and reliable mobile connection wherever they live - and we continue to work with the industry as they gradually move away from 3G to ensure ensure that customers do not do that." so that you do not lose access to a suitable network.
"4G coverage is already available in 93 percent of the country, and we are spending £1 billion to end patchy connections in rural areas.
"By 2025 we expect coverage to increase to 95 percent of the UK landmass and we are on track to achieve this target."
A spokesperson for the mobile networks said: "Mobile phone coverage is affected by a number of variables, including weather, seasonal leaf growth, the way buildings are constructed and local topography.
"Ofcom coverage reports act as a guide to coverage."
They added: "The phased switch-off, with 3G switched off first, followed by 2G, will ensure the transition is as seamless as possible.
"2G networks will continue to provide access to calls and text messages, while the repurposing of the spectrum used by 3G for 4G and 5G services will deliver a vastly improved service, providing capacity, the full mobile internet and additional service capabilities will be added."
A Vodafone spokesperson said: "This change will allow us to move the 3G radio spectrum to enhance our 4G and 5G services in the UK.
"If any of our customers still have concerns, we ask them to contact us."
'We are closely monitoring the process'
An Ofcom spokesperson said: "Mobile operators have decided to switch off 3G to make way for faster 4G and 5G services, and two of them have already completed this.
"We have set clear expectations for suppliers to minimize the impact on customers, and we will continue to monitor the process closely.
"The coverage data that mobile operators provide us gives us a good picture overall, but offers no guarantee. We regularly carry out tests to ensure that operator predictions are as accurate as possible."
