My suggestion would be for an SMC barricade. I paid about £70 for an SMC7004BR a couple of years ago. They've been replaced by newer, better, and cheaper models now though, so it's got to be worth checking them out. They are fairly cheap, but they have nice features like print servers, dial-up fallback, etc.

Also, tell us if you're getting a cable modem (blueyonder/NTL), ADSL (almost everyone else), or wireless (not very common in the UK at the moment), as this will influence your final choice of router a hell of a lot. If you're getting ADSL, it might be cheaper for you to get a combined ADSL modem/router instead of seperate devices.