BT say (https://www.bt.com/broadband/digital-voice):

I have been chuntering away for quite some time, I don’t think there’s any resilience in the new fibre optic system that’s replacing the copper telephone network, you will need to use the internet through the cellular network if there’s a power cut.

Take as an example the emergency pendants the old ladies have, they have to go cellular personalalarms.ageco.co.uk/.../taking-care-anywhere-4327

Out here in the sticks, I have a pole transformer supplying just my property. When they nstalled a broadband cabinet up the hill they took a supply from the same transformer so when I'm off, it's off.

There is a discussion here: https://community.bt.com/t5/Home-phone-including-Digital/Mains-power-cuts-and-DigitalVoice/td-p/2217183

Interestingly, there is a suggestion that lack of power at the street cabinet, while a problem for FTTC (Fibre To The Cabinet) , might not be either for analogue phone lines (line power is passed through passively from the exchange) , nor with FTTP (Fibre To The Premises) - as the optics again run straight through to the exchange (I'm not sure if that's true or whether the cabinet still has some reshaping/amplification role). Seemingly the cabinets have battery backup which should last for at least 4 hours - after than the batteries may be replaced (but perhaps unlikely if the outage is widespread).

  - Andy.

My mum's got a pendant, it talks though a box connected to the phone line.  Of course, that means it will only work at home.

There should be ones available now that connect through the mobile phone network.

Land line phones are pretty much obsolete now, like fax machines and dial-up modems (which also rely on analogue phone lines).  I only use mine for freephone calls.  For everything else, I use the mobile.

When I was a kid in the 1960’s we lived opposite Council owned “old folks” bungalows, each home had pull cords in the bungalows connected to a bulkhead light fitting on the front of the bungalow that had a red bulb in it.

Every evening before going to bed my mother would look out of her bedroom window to check there were not any red lights on, because the system relied on there being neighbours like her checking throughout the day and night.

There used to be similar setups up and down the country, it could be the level of technology we are going back to with battery operated lights as a backup to all the internet connected stuff.

The advice to use a mobile phone is a classic example of the left hand does not know what the right hand is doing. A great many of the newer base stations (that all mobile phones require)  are not battery backed up and depend, guess what, on the local  substation for power ! 

It is true that some larger base stations (generally the ones that serve as a hub to a group of base stations or share a site that already has back-up) do have some battery arrangement or even in a few cases self starting diesel generation, but to install proper back up power has not been a requirement for some time, and so now tends not to be done.  Now it may be that the failure of one substation  can be called in, because there is a  base station in range of the handset which happens to be on another LV transformer, but rota power cuts would appear to be based on the HV areas, and so larger areas of many tens of miles across all go off together. Only folk at the very edge  of zone can expect a mobile phone connection of any kind, and ones running on emergency power are designed to drop back to a low power mode with reduced performance, and in some cases emergency calls only. In a cut of any duration, you may be able to contact more people by carrying   a hand bell or whistle.

Actually  some folk have been wondering abut this for a while... https://forums.digitalspy.com/discussion/2121314/mobile-netwroks-and-power-cuts

Mike

The street side cabinets DO NOT have any special or protected power supply. Providing this would be impractical. Neither do they have any supply from the exchange.

They do have backup batteries, I have limited faith in these.

mapj1 said:

you may be able to contact more people by carrying   a hand bell or whistle

We didn't always have telephones. There was a time when if somebody was taken ill, they would get a lad to run to the doctor. Of course doctor would have been one of the first to have a telephone, but that still wouldn't have helped ordinary folk without one.

I suppose that if you are nervous about the situation, you could get a satellite 'phone.

I've been doing a little research and as far as I can tell, the FTTP (fibre to the premises) system doesn't seem to rely on the roadside (green) cabinets at all - and all the gubbins between exchange and home seems to be entirely optical and passive and so don't need any power. There's an interesting video here: https://youtu.be/6595-Xv-pZk

So as long as there's some kind of UPS at home, and the exchanges still have their usual backup supplies the situation might not be that bad after all. I know that a lot of existing "fibre" installations are just fibre to the cabinet (FTTC) - but judging by all the new fibre boxes that have just appeared on top of all the local telephone poles around here, FTTP seems to be the way things are going.

   - Andy.