Estimates of Working Tax Credit take-up rates for singles and couples without children for 2005-06, which are the latest available estimates, are provided in table 13 of the HMRC publication “Child and Working Tax Credit Take-up rates 2005-06”. This publication is available on the HMRC website at:
http://www.hmrc.gov.uk/stats/personal-tax-credits/cwtc-take-up2005-06.pdf
The Government are taking steps to ensure that childless workers claim and receive the support they are entitled to. The 2008 pre-Budget report announced proposals including HMRC aiming to double its partnership marketing coverage of Working Tax Credit (WTC) in the coming year.