> Over here a common theme is portraying the average family as mixed race despite the fact that the vast majority of UK families are not mixed race at all.

It's cheaper to run 1 ad instead of two, to capture 2 demographics. In America, a mixed-race cereal commercial caused an uproar around 10 or so years ago. You wouldn't have thought so, but family representations on TV that veer from majority culture status quo appear to be a sore point for some.