Yeah - depends what you want to achieve. If you just want to be evaluated, Computer Music and Future Music (they're British mags - I take it you're also British, being called Brummy Git and all) both have reader demo sections, and they comment on everything sent in, but it can take up to about six months before your demo makes an appearance.
If you actually want to go about getting signed, first thing you should do is trawl your collection for records in a similar vein to your own stuff and make a note of the labels. Then look them up on the internet (most record labels have websites), find yourself some contact details - anything will do, even the standard 'info@...' email you'll find on most sites - get in touch with them, let them know who you are and what you're about and then wait for a reply. If you're looking at indies (and if you're unsigned, you need to be), they will generally get back to you if they're interested. It's best to actually get some kind of response from them before you send anything out, because they might tell you specifically who to address your demo to (plus, of course, it establishes some kind of rapport with them, which can never be a bad thing). Still, if you don't hear anything from them after a few days, just send your demo anyway.
Mind you, I'm still not signed yet, so chances are, I could be talking crap.