DramatisingtheviolentreignoftwoofLondonsmostnotoriousgangsters,BillyHill(LeoGregory)andJackSpotComer(TerryStone),ONCEUPONATIMEINLONDONchartsthelegendaryriseandfallofanationwidecriminalempirethatlasteduntilthemid-fiftiesandwhichpavedthewayforthenotoriousKrayTwinsandTheRichardsons.