"I can't leave TescoWeb, I don't want to change my email address"
That didn't stop Vodafone closing the Demon email service (and web space) and handing control to an external supplier on a separate subscription basis. Vodafone didn't reduce the Demon subscription in recompense either.
Now Vodafone are shuttering Demon completely. That presumably means personal home servers visible as <mydomain>.demon.co.uk will also now become unavailable. Presumably you will have to buy your own domain to map onto a (new?) Vodafone static IP address.
The email they have sent to Demon customers is totally lacking in any meaningful information.