Estimates of the numbers of families with tax credits awards, including information on overpayments and underpayments by constituency and county, based on final family circumstances and incomes, for 2005-06, is available in the HMRC publication "Child and Working Tax Credits Statistics. Finalised Annual Awards 2005-06. Supplements on Payments in 2005-06. Geographical Analysis", which is available on the HMRC website at:
http://www.hmrc.gov.uk/stats/personal-tax-credits/cwtc-geog-stats.htm
Estimates for 2006-07 tax credit awards are due to be published in May 2008 when family circumstances and incomes have been finalised.