huit

You're in the UK - there's a lot of excellent race tracks all over the country with a lot of car clubs that cater for all kinds of cars. Track days in Asia (eg HK etc where the nearest track is in Zhuhai) is still very expensive and remain a pastime of the affluent, whereas in the UK it is much more affordable so don't waste this opportunity.

I would suggest joining a club and go on a few track days. Trust me, spend the amount of money on improving yourself as a driver will make you go much faster than if you were to spend the same amount on modifying the car. And you'll be able to track your progress and the skill will stay with you.

Once your skills have improved then you'll be able to better identify what areas of the car you need to modify to go even faster.