There is now "sufficient evidence for a realistic prospect of conviction" of PC Alex MacFarlane, a Crown Prosecution Service review concluded.
Lawyers studied footage appearing to show the officer say to a 21-year-old black man: "The problem with you is you will always be a n*****, yeah?".
More top news
A police officer who spent six days crawling the London Marathon in a gorilla costume has finally completed the 26-mile route.
The victim of a "violent and sustained attack" on the top deck of a London bus has been named as Archie Sheppard.
Transport for London has made the badges and accompanying cards permanently available after a successful trial in autumn last year.