"I am also toying with the idea of just getting a £10k loan and having a 400 build and all the refineries to launch, stop and keep me in straight line done.... "

10K will be about half of your budget if you want to make it a good spec

Front diff £1300
Rear diff £750
Decent Box is £3500
Decent set of Front brakes £1400
Suspension- £1000+
Stainless Mongoose Exhaust £400
Rear beam £650
Clutch- £350+

Then you start on the engine, the coolers, the pipes, the turbo and the build of the actual engine....
Belive me, I'm doing the same thing...

then dont forget bits like mapping, teething troubles etc etc

BUT, you will have a fucking superb fastroad / occasional track/strip car