In 1940, NUCAW merged with the Association of Women Clerks and Secretaries (AWCS) to form the Clerical and Administrative Workers' Union (CAWU).

The union organised in the white-collar sector in the City of London and across the country, and had particular success in recruiting in the engineering industry.

[1] The union changed its name to the Association of Professional, Executive, Clerical and Computer Staff (APEX) in 1972.

APEX, like its predecessors, was an affiliated trade union of the British Labour Party and was a key influence on the right-wing of the Party, particularly as, until 1972, it enforced a rule preventing communists from holding positions in the union.

The union sponsored numerous Labour Party candidates, many of whom were elected: