Working for yourself
https://www.gov.uk/working-for-yourself

Set up as a sole trader
https://www.gov.uk/set-up-sole-trader

Set up a private limited company
https://www.gov.uk/limited-company-formation

Running a limited company
https://www.gov.uk/running-a-limited-company

Accounts and tax returns for private limited companies
https://www.gov.uk/prepare-file-annual-accounts-for-limited-company

Businesses and charging VAT
https://www.gov.uk/vat-businesses

Expenses if you're self-employed
https://www.gov.uk/expenses-if-youre-self-employed

File your Company Tax Return with HMRC
https://www.gov.uk/file-your-company-accounts-and-tax-return

Simplified expenses if you're self-employed
https://www.gov.uk/simpler-income-tax-simplified-expenses

Self Assessment tax returns
https://www.gov.uk/self-assessment-tax-returns

The Pensions Regulator
http://www.thepensionsregulator.gov.uk/