mike holpin , from ebbw vale in monmouthshire , has at least 40 children .
ca n't name half of them and has family tree tattoo to help him remember .
around 16 were taken into care ` because of my drinking and womanising '
but 56-year-old wants more because he ` ca n't live without them '
` in the bible , god says go forth and multiply . i 'm doing what god wants '
holpin has not worked for a decade and said to receive £ 27,000 in benefits .
documentary also shines light on 29-year-old father of 15 from sunderland .