If you are, or are not quite sure then best take a look at HM Revenue & Custom's recent "e-market places campaign". 

Broadly, if you are trading online, and have not told HMRC about this income, you may have under paid tax, and by using HMRC's "e-Markets Disclosure Facility (e-MDF)" by 14 June 2012 then you can have matters brought up to date on "preferential terms".   Use the following link to read more:

http://www.hmrc.gov.uk/campaigns/emarket.htm

Buick & Co Chartered Tax Advisers and Tax Consultants take no responsibility whatsoever for this blog, its reliability or any actions you take having read it.