Im thinking of setting up an online business, what do I need to know about tax?

Im 17, I currently have no other income, I have an idea for an online business, how much do I need to be earning to pay tax? and if do I need to register my business or anything?

Any advice would be much appreciated

Sorry should have mentioned im in England.

hi, these guides from HM revenues & customs should tell you all you need to know about tax issues http://www.hmrc.gov.uk/selfemployed/tmas...
business link also have some guides on income tax for the self-employed http://www.businesslink.gov.uk/bdotg/act...
Small earnings exceptions - If your earnings are less than 拢4,635 for 2007/08 you can apply for a certificate of small earnings exception by completing form CF10 from HMRC.
however you should speak to the National Insurance Contributions Office or a local citizen's advice bureau before you do this as it could affect your entitlement to certain benefits if you ever need to claim them.

Go to http://www.score.org/index.html and in the upper left hand corner, enter your zip code. On the next screen, you will get information on the nearest SCORE chapter. Call them and arrange for a free meeting with a SCORE counselor to discuss starting a business and its tax implications.

SCORE is a nonprofit association dedicated to entrepreneur education and the formation, growth and success of small business nationwide. SCORE is a resource partner with the U.S. Small Business Administration (SBA).

SCORE has 389 chapters in locations throughout the United States and its territories, with 10,500 volunteers nationwide. Both working and retired executives and business owners donate time and expertise as business counselors.

You need to register as self employed with HMRC - go to www.hmrc.gov.uk for how to do that. It probably would not be worth registering as a company right now.
I think you should take some advice from an accountant about record keeping to make sure you have enough info for your tax return.