How do you make money.

[Nigel]

....a profit of around £220, £300-350 if I eat packed lunches and dont buy food.

I am by no means an expert on money, but this one statement popped an attention sign in my mind.
Don't try to save money by buying cheap food - which could compromise your health if you do it for too long.

Don't get me wrong, I am not telling you to go to expensive restaurants of eat fancy stuff. But just don't go cheap on your health; you may come to regret it in older years. There is a lot of good quality food that you can buy for a reasonable price, fresh vegetables, fruit. Buy meat less often, but get it in good quality from the butcher's. It is really not that much more expensive, but buying good quality food should come before making a profit.

Other than that I can only echo what others have said:
Don't spend more than you earn, stay away from building up debt.
And later, most of your wealth is likely going to come from your work - not from your investments. So focusing on your studies to get good grades and a good job afterwards is really the best investment you can make.