http://www.companieshouse.gov.uk/
Ltd. Company is often £30 or less (PM me if you want sample association papers), only go sole trader if you
can't keep financial records or cant afford the initial £30.
Risking a crappy life for a business idea is almost always a bad idea.
You will also almost certainly
need the services of an accountant if you run a Ltd. Company.
Others may argue, but I would never put my life on the line for money.
PS if you are under 16, any debts may even be accountable to your parental guardians.