HM Revenue & Customs: http://www.hmrc.gov.uk/index.htm
Visit the site for information on contacting a government tax advisor. HM Revenue & Customs can also answer questions you may have about paying tax as an expat in London.
The Institute for Chartered Accountants in England and Wales: http://find.icaew.com/search/town/London/country/england
This is the professional body that supports accountants in England. Find an accredited accountant on this site.
http://www.ukexpat.net: This site can direct you to the help you need to resolve any expat tax issues.
HSBC: The world’s local bank- has an informative site, written in simple terms for a very complex subject: http://www.expat.hsbc.com/1/PA_ES_Content_Mgmt/content/hsbc_expat/pdf/en/global_tax_navigator/going_to_the_UK.pdf
The accounting department at your company will also be able to provide contact details of local tax authorities as well as be able to recommend qualified tax advisors and accountants.