The telecoms giant has admitted that some personal health alarms and burglar alarms – which use landlines to dial the emergency services in case of a fall or home break-in – will cease to function once copper lines are switched off. These services must be upgraded or replaced and customers must cover the cost themselves.

Those affected are already being forced to take action to ensure they are not cut off and left unable to call for help. Alison Thompson, a 70-year-old small-scale farmer from Anglesey, said she planned to buy a small generator as a fail-safe to keep her electricity going in case of a storm after her phone lines were moved to the digital system in June last year.

She said she needed an accessible line to the vet all the time during lambing season and the backup solutions offered by BT were insufficient.

“I am well used to power cuts over the winter. Most last six to eight hours, others longer,” she said. “What I am not used to is being unable to use my landline. I am 70, live alone and keep sheep. It is frequently necessary to call a vet for a difficult lambing or other emergency and they need to call me about their arrival time. There is a poor or non­existent mobile signal here and an emergency battery pack lasting little more than an hour is of little use.”

Others face similar difficulties. A 54-year-old reader from a rural part of Lancashire said he also planned to buy a small petrol generator to keep the power on in his cottage. He said he needed to be certain he could call for help during bad weather in case his 89-year-old mother, who has dementia, fell ill. He said the cheapest solution he could find cost around £190.

John Landamore, 60, from rural Leicestershire, said he faced the cost of replacing his wife’s “Telecare” personal alarm system with a more modern set-up as it relied on landline technology.

“My wife is paralysed after she suffered two strokes. She is immobile and is completely dependent on me. She needs the alarm in case of emergency and for when I am not there,” he said.

Trevor Bullock, 81, said he faced paying as much as £500 to replace his ADT burglar alarm system, which uses older landline technology to call the emergency services in the event of a break-in or fire.

“On contacting my supplier to ascertain the impact, it appears the solution is to either convert the existing analogue equipment or replace the whole system – either would be at a cost of several hundred pounds,” he said.