In 1921, the two series were merged into Notable British Trials and the red binding and gilt lettering became the uniform identifying feature. Between the wars cheaper editions were also sold bound in red cloth with black lettering.
In 1921, the two series were combined into "Notable British Trials," and the distinctive red covers with gold lettering became the standard identifier. During the interwar period, more affordable editions were also sold with a red cloth cover and black lettering.