I agree with whats been said so far really. Depending on what you what to get out of the car. If you want a track car just make it light as possible, get coilovers, arb's, roll cage make that chassis stiff as hell. Get a decent brake upgrage. Then learn to drive on a track Ie cat driving school.
If you what power to burn porkers and m3's etc, look at boost, APS TT kit from the states will set you back about $7k so £5kish then double that (at least) to fit it and tune it etc. Then don't expect to use it everyday, the more power you put in the more that will go wrong, clutch wont last long, and other parts won't last as long so it'll be in the garage more than you think.
Or if you what what most of us want, a great looking car that's faster than most but not all. Make a few exterior mod's, get a nice sounding exhaust, CAI, plemum spacer, upgrade the brakes slightly, you'll have a very nice looking everyday car. Even look at a ecu upgrade to bring the mods together but won't be reaching 300hp