In 1921, the first standard kiosk appeared, the K1. The K1 was intended for rural areas and was made of concrete. In the late 1920's the Royal Fine Arts Commission on behalf of the GPO invited a few people to design a new kiosk. In 1926 the chosen design appeared, Giles Gilbert Scott's K2. The K2 was of cast iron construction and a few hundred remain today. The K2 was too big and too expensive for mass production. The GPO wanted a new design and asked Sir Giles to produce another design, in 1929 the K3 appeared, a smaller, concrete version of the K2. In 1927, the K4 was intended to be a 24-hour post office with a stamp machine and letterbox added to the back. It was nicknamed the Vermilion Giant and was a fantastic failure with only 50 produced. In 1934, a K5 was produced, made of plywood as a temporary kiosk for use at exhibitions and fairs etc. With problems occurring with the K3, a new cast iron box was needed and in 1936 the K6 appeared for the first time on the streets. The kiosk was perfect, it had all the good points of the K1 and K3 mixed with the solidness of the K2 and most importantly, the small size and elegance the Post Office were looking for.

The K6 also known as the 'Jubilee kiosk' was widely used to replace K1's and K3's. In the 1960's the Post Office were considering a new design. Neville Conder's design for a K7 was chosen. It was made in aluminium and was tested in 1962. The K7 was not adopted as a new design and only five were made. In 1965, another competition was held to design a new kiosk, the K8. Bruce Martin was the winning architect and his design appeared in 1968. It was a very new design to the previous ones. The main differences were that the glazing bars had gone to be replaced with just one big window on each side of the kiosk and the domed roof was replaced with a much flatter design. Nearly 4,000 K8s would appear, some of which replaced K6s.