I was looking at the website of my new electricity/gas supplier and found an 0845 number:

https://support.avroenergy.co.uk/hc/en-us/articles/360006569538-What-if-I-have-a
-power-cut-

08456589655

I can't see that I'm likely to need it but it's still wrong that it's there, and with no declaration of charges.

It's not in the SayNo database. Googling suggests that it's probably a number used by Lowri Beck, who do a lot of work on metering etc. LB's contact page: https://www.lowribeck.co.uk/contact gives 01942 772060 but no idea if that would reach the right part of the compnay in an emergency.