In the workplace, the Positive Action exception is for
"proportionate action that aims to reduce disadvantage, meet different needs and increase participation"
or
"actions that reduce disadvantage and/or increase representation specifically when it comes to deciding between equally qualified candidates"
for people who share a PC and who the employer can show are currently disadvantaged or underrepresented in the company or in that line of work.
So the friend who runs a big company with schemes to help "ethnic minority people" and "women" would have to have separate positive action schemes for women generally and for ethnic minorities. The ethnic minority in each scheme would all have to be of the same ethnicity or race or national origin (or combo of national origin/race/ethnicity). Black African, Afro-caribbean, British Asian, Ukrainian, Jewish Scots, Welsh, Irish Travellers, Roma would all be fine. I don't think the friend would be able to cite BAME as a single group for positive action, from what I've read in the EHRC guidance, but I'm not sure.