RIP
I was a Demon customer in the relatively early days, I remember they had 071 and 081 (or 0171 and 0181, can't remember when the 1 was added) and a Warrington number, presumably as that's a local call from Liverpool and Manchester, or something like that.
We had an account at work first, since we worked for a large American telecoms company that was completely incapable of providing internet access (I think they wanted to cross charge 30p per k or data or something like that). Another department had one too and did a website before the corporate marketing antibodies stamped it out in another front of marketing's perpetual war on information.
I actually used Demon from home on a Mac, Demon provided a book with a disk with software - this was (just) before Netscape came out so I am thinking early 1994. I remember listening to World Radio Network (is that still going?) using RealPlayer on a 9600 baud modem. Amazing, really.