What to study at University?
Firstly, university is not the only route in life. There is off course the apprenticeship route, self-employment (starting your own business), trades, professional qualification such as ACCA or CIMA for accounting, etc.
University in an investment of 3-4 years of your life, and may I emphasise prime life as you are only young once. Further, it can be a large financial investment costing in the region of £27,000 to well it depends on accommodation, books and how much you party. Not to forget the lost income since you are studying full-time and not working. Some would suggest that £27k is an amount large enough to start your own business but I suppose you need to know how to run a business otherwise it could just as easily fail.
Selecting the right subject at university is important especially if you are aiming for certain jobs however some employers are more interested in how well you performed regardless of the subject. For example certain jobs in banks, business consultancies would happily employ somebody with a History, Geography degrees as long as they have the right grades. Although if it is a technical job such as IT or analytics then it is obvious that only an IT degree or Math, Economics, and Engineering would suffice respectively.
Hope this helps. Feel free to ask a question.
Disclaimer- Please do seek career advisor's advice as this is an important decision.