http://www.caterham.co.uk/asse ... l/experience/circuit.html

Im interested in the full day, the two closest circuits (no more than 2 hours drive) are Silverstone and Oulton Park

But which one should I choose?

I have only drivin on a race circuit once before, Formula Ford 1800cc around Donnington, but there wasn't much training involved other than a few laps in an MG with an instructor (who thought it wasn't my first time as I was heal-toeing).

Or does anyone have any other suggestions?

Oulton Park, without a shadow of a doubt. Silverstone is too wide and boring for anything slower than a GP2 car. Oulton will provide more fun, more challenge, and will be a lot more relaxed during the day.

Don't worry about training - just don't try and drive above your ability. Concentrate, like in LFS, on smoothness and consistency rather than speed. Don't press the throttle until the car is ready for it, and feed it in as you wind off the lock on corner entry (at least until you're confident in the car, track and your ability). Brake earlier rather than later - late brakers end up crashing or being slow, early brakers end up nearly as fast as optimum brakers and have a bit of leeway for mistakes.

Most of all just enjoy yourself.

I agree -- Oulton is great and pretty scary too. Silverstone is a bit too open unless you have masses of power.