First contact your insurance company and see what they have to say about a hike in power. Do not under any circumstances not disclose info to them as if it goes wrong you could be in a whole world of shit.

Assuming the car is standard I would start with the brakes and suspension (these on the road will be like endowing your car with another 30bhp as you will be able to corner faster and brake later). My personal choice would be Koni shocks and Eibach springs with a strut brace (budget on £600). At least a disc and pad combo for the brakes something like Tarox 20 groove discs and Mintex pads (Budget £250)

Decent wheels and tyres will improve things dramatically. Avoid rims bigger than 16" as it will proove detrimenatl to the cars handling (budget £800)

From there you can up the power. Start with a decent full exhaust from a company like Magnex (£255) and a K&N panel filter in the original air box (£35) Drill the airbox to aid air flow but also restrict warm air being drawn in like with a cone filter (free!).

You'll now be about £1900 down on your budget or more if you have these parts fitted for you but you will have your basics and will get you going nicely from there you may want to talk to tuners but at least you will have a chassi sthat will cope with all the extra grunt you are likely to throw at it.