Saying the figure "ought to have been 1 in 13 based on the study's upper figure for irregular migrants, which includes children born in the UK w/irregular status, and, it is understood, those w/ILR" implies that people (or children, it's not clear) w/ILR are illegal.
Saying the figure "ought to have been 1 in 13 based on the study's upper figure for irregular migrants, which includes children born in the UK w/irregular status, and, it is understood, those w/ILR" implies that people (or children, it's not clear) w/ILR are illegal.