Source: Office for National Statistics

Link: http://www.ons.gov.uk/peoplepopulationandcommunity/birthsdeathsandmarriages/livebirths/datasets/birthsummarytables

A birth within marriage/civil partnership is that of a child born to parents who were lawfully married/in a civil partnership either, a) at the date of the child’s birth, or b) when the child was conceived, even if they later divorced/were granted a civil partnership dissolution or the father/second parent died before the child’s birth.