Ebay was good tgo me again today. Four powerline adapters arrived, TP-Link 411. This could be an alternative for connecting the server room to the rest of the house.
They work by sending a high frequency signal along the main electricity system. But will it work on my system? There isn't just the one circuit. Also, there are three phases. So I don't know. But I paid only £15 for four units.
The way to find out, of course, is going to be - suck it and see.