A few useful links …
HM Revenue & Customs – vast amounts of ever-changing information
The Institute of Chartered Accountants in England and Wales (ICAEW) – not terribly interesting unless you’re an accountant!
Companies House – the central register of UK companies
The Law Society – the regulatory body for solicitors, with details of local practitioners, how to complain, etc
The Charities Commission – essential information for those involved in charities
UK Government Business Help – lots of useful information for those setting up in business