HMRC
Tax Credits
Online Calculator
For general information about tax credits
Opening hours
8.00 am to 8.00 pm, Monday to Friday
8.00 am to 4.00 pm Saturday
Closed Sundays, Christmas Day, Boxing Day and New Year's Day
0845 300 3900
Child Benefit, includes link to claim form
http://www.hmrc.gov.uk/childbenefit/index.htm
Will add to this............
Citizens Advice