It was designed by G. J. Rackham, an employee of the American firm Yellow Coach from 1922 to 1926, leading him into contact with the Fageol Twin Coach. It was not until a visit to America in the late 1920s that Rackham noted the success of the 1925 Twin Coach which had won large sales to American operators. The result was Rackham returned to Southall (AEC's Works) with the idea of implementing American practice of side mounted engines in British bus production.
The Q-type, although based on the Twin Coach, had many differences. The most noticeable being whilst the Twin Coach had two engines (hence the name) the AEC Q only had one. This overcame the many complications a second engine needed in the transmission. London General Omnibus Company received the first Q-type vehicle with a crash gearbox although all subsequent vehicles had the pre-select version. The engine was available in either petrol or diesel incarnation and was located longitudinally behind the front axle, intended to be hidden by the staircase (for double-deck version). This allowed the drivers cab to be located on the front overhang with the entrance opposite, even though some body builders didn't use this facility and had a centre entrance. Being a more modern design, it looked very similar to buses built in the 1950s and 1960s.
The Q failed to attract the attention of the British operators and as a result failed to find a market in the UK like that Fageol had found in the US. One of the reasons was the Q was prone to problems, the most concerning being that the petrol models caught fire at the carburetor. The recommended solution was just as worrying… increasing the revs until the fire went out! The result being the Q did not obtain the popularity of the other AEC models so the project was dropped, last appearing in the 1937 catalogue.