Trademarks etc is a very complicated area, but you'd be well advised to check here for starters:
Intellectual Property Office - Welcome to the Intellectual Property Office
You can search through the relevant categories to check whether anyone is using the name/phrase already. However, just because someone hasn't trade marked something, it doesn't mean you can use it as you please. There's all kinds of issues like who started using it first and what industry the two parties operate in.
Definitely do some reading up on the subject because it can be a very costly mistake if you get it wrong. If you can trademark something, it's usually worth it because it just gives you a bit of extra protection should push come to shove.