The Office for National Statistics (ONS) and HM Revenue and Customs (HMRC) use different definitions of lone parents and the statistics they produce refer to different time periods and are therefore not comparable.
The tax and benefit system defines a couple as either a man and a woman who are either married or ‘living together as husband and wife’ or two people of the same sex who are either civil partners or living together as such. The Labour Force Survey (LFS) asks about the adults living in a household, and it counts an adult as being single if they do not declare another adult in the household as being their partner.
ONS estimates that there are 1.9 million lone parents in the UK, based on the 2006 Labour Force Survey data. The HMRC 2005-06 Finalised Award data show that on average 2.1 million families claimed child tax credit, or the equivalent via benefits, as a single adult.