The BR Standard class 6 Pacific was designed after the Standard class 7 “Britannia”. Since the Britannia was too heavy for many lines in Scotland, a new type of locomotives with a better route availability had to be ordered. Trials with the SR Bulleid Light Pacific on the line to Inverness had shown that a light Pacific would be optimal for this task. So Riddles took the frames of the Britannia and mounted a smaller boiler with a pressure of 225 instead of 250 psi and smaller cylinders.