Need some forms? Or reference sites for Frequently Asked Questions.
Try these links:

Inland Revenue
The Inland Revenue's web site gives access to their latest press releases, self assessment information, leaflets, office locations, FAQs & many advices.
www.inlandrevenue.gov.uk

HM Customs & Excise
HM Customs and Excise is responsible for collecting and administering Customs and Excise duties and Value Added Tax (VAT).
www.hmce.gov.uk

Companies House
Companies House deals with the incorporation, re-registration and striking off of companies and the registration of documents required to be filed under companies and insolvency acts.
www.companies-house.gov.uk