My Mum has a fall alarm that uses the land line to call for help. There's no mobile phone reception in her house on any network, so she needs the landline to call for help occasionally. It's not unusual to have power cuts and some last for several hours, probably the most likely time she needs the landline to work and I gather the current backup options will only last for an hour.
Just an update on this. Mum has received an update from BT that didn't give much info but stated she will get an upgrade but there's no need to change equipment.
A quick call to BT has confirmed they are upgrading her exchange to turn the digital signal to analogue to send down the existing copper cable. I gather the technology is SOTAP and it means her line will stay old copper for a couple of years so her alarm should still work.
Hopefully the exchange will have backup power...