You're probably thinking of Charle Alliston who killed someone on Old St and got 18 months for it - to be road legal, fixed-gear bikes must still have a front brake, and have at least since the fifties, A fixed gear counts as a back brake but you must have two for redundancy.
This. Most cyclist fatalities in London are caused by Heavy Good Vehicles illegally overtaking and then turning and therefore trapping the poor cyclist in the blind spot.
Nothing to do with the wheel hub design or bicycle braking system.