A spectator dressed as a policeman laughs outside Westminster Abbey on the eve of the Royal Wedding between Prince William and Kate Middleton in London. (AP Photo/Owen Humphreys-pa)

Each step has been rehearsed, each flower meticulously arranged, the aisle of Westminster Abbey transformed into a flowering green avenue of trees.

As Kate Middleton and best man Prince Harry had a final run-through inside the abbey where she will marry Prince William today, a growing throng of curious tourists, dedicated monarchists, souvenir vendors, William-watchers and Harry-hunters turned the Union Jack-bedecked streets outside the iconic landmark into a scene of festive chaos.