HMRC First steps to register as self-employed:
http://www.hmrc.gov.uk/selfemployed/register-selfemp.htm
CAB Self-employment check list:
http://www.adviceguide.org.uk/index/your_money/employment_index_ew/self-employment_checklist.htm
Business Links Guide:
http://www.businesslink.gov.uk/bdotg/action/layer?topicId=1073875654