Millions of the UK's elderly and vulnerable households face being isolated in a digital revolution of BT's landline service.

Pensioners groups have criticised the move by BT to force all homes online amid concerns for those people who rely on traditional Landline Phones to communicate.

BT's digital changeover, which will come into effect in 2025, will see the traditional handset replaced by a new 'digital' phone, which is powered by electricity, that relies upon the internet for calls to be made.

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But Jan Shortt, general secretary of the National Pensioners Convention, said: "If there is a power cut, this digital phone line will no longer work – and a potential lifeline for elderly people will be suddenly lost.

"Those needing to make an emergency call or raise an alarm via a health pendant could be left stranded – and unable to call anyone to ask for life-saving support."

Around six percent of households – roughly 1.5 million homes – do not have access to the Internet, according to watchdog Ofcom.

Those homeowners may need an engineer to visit their to get them set up and those with older phones could need to buy a new handset.

But experts fear millions more do not have a mobile phone or do not know how to use one properly.

Ms Shortt said: BT has no idea that many older people do not want a fancy smartphone or cannot afford one – and rely on their landline as a lifeline. It is wrong to discriminate against those – primarily the elderly – who are not wired up to the internet.'

Caroline Abrahams, director of Age UK, said: "Given that about half of older people over the age of 75 are not online, this could be a particular problem for our oldest citizens."

Ofcom has stressed that telecoms providers have an obligation to ensure these households have access to the emergency services, which may be fulfilled by providing a free mobile phone to customers.

Unlike the switch to digital TV in 2012, this change is said to be driven by the telecoms industry and not the Government.

Openreach, which runs the majority of the nation's wire and cable infrastructure, has been working with businesses for months to ensure they are ready, and has stressed that protecting vulnerable customers is "an absolute priority".

And the firm is aiming to install ultra-fast full fibre broadband in 25 million households by the end of 2026, which should provide a more reliable service.

There are an estimated 1.5million homes in the country that don't have internet access.

BT's switchover, branded 'Digital Voice', began two years ago and has so far converted two million landlines.

But with an end-of-2025 deadline for switching 29million home landlines, there are fears that the new system's flaws will be increasingly exposed.

Under guidelines laid down by Ofcom, BT must ensure customers can contact emergency services in a power cut that lasts more than an hour. But how this can be achieved if you lose access from an internet phone line or do not have a mobile phone – or signal – is not clear.

In addition, charity Age UK is fearful the changeover could attract criminals claiming to be involved in the switch.

Caroline Abrahams says: 'We are concerned the changes could make many elderly feel more isolated than they do already. Steps must also be taken to ensure the vulnerable do not become victims of any digital voice scams."

Homes already on the internet should find the switch relatively straightforward. But the minority who do not already have an internet connection will have to be wired up to accept the new digital phone technology.

This will involve an engineer visiting for free to fix 'digital voice' sockets inside your home.

BT says claims customers should not see prices rise due to the change. Those already signed up to an internet service will see the landline charge included as part of the total bill – whether they use BT or a competitor.

Those just paying for a landline and not using the internet will be charged separately and not pay more.

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