The oft-mentioned alternative when power cuts are discussed on the 'Home Phone' forum in regard to 21CV landlines is to 'just use a mobile' but, from my tests yesterday, the mobile network stopped working too (for ordinary calls and data).
Presumably the 999 functions of the mobile network would still have worked. For those with older family members, who might want some help or reassurance during a power cut (especially one which went on for several hours), there was no practical way to get in touch for those groups (who probably could not use text messaging under such circumstances, if at all).
There has also been a few topics on 'Home Phone' from those with medical/care alerts (which dial a general call centre number) who may also have run into difficulties as those devices (dialling general landline numbers) presumably would also have failed to work, even via the mobile network.
I'd be interested to know, from any of the regulars on the forums who are from within the industry, whether the fact that the mobile network ceased working for all but texts was actually by design during a big power cut (to prioritise emergency calls etc.) or simply that the mobile network is not that resilient and if the area of the power cut is big enough, then the mobile network stops functioning for normal communications.