The concrete Kiosk No. 1, as introduced in 1921. It was made up in sections of reinforced concrete and fitted with a wooden door. The upper portion had glazed panels on the two sides and front. The three concrete sections fit into the base and top, all joints being filled in with cement. The first model, the Mk234, had wooden window frames. These were soon replaced by metal frames, in the Mk235.

The first standard kiosk - the Kiosk No. 1, or K1 - was a simple design. Little more than a modified Birmingham pattern, albeit made of pre-cast concrete, it did little to encourage the many local authorities to allow it on to their streets. The Post Office chose the proposed sites with great care, with situations off the main pavement being preferred. Frequently they resorted to striking a deal with a private landowner. They would even paint the box in whatever colour the local authority wanted. Even so, some were not to be persuaded and notable amongst these were the Metropolitan Boroughs, which controlled the central districts of London.

One concern was that telephone boxes were an obstruction to the thoroughfare and yet, somewhat oddly, what appeared to be called for was something grand and imposing. In 1923 the Metropolitan Boroughs Joint Standing Committee organised a design competition. The entries were disappointing and, in any case, more general discussion had begun. The Birmingham Civic Society had submitted a design to the Post Office, which had itself been busy, both with improvements to the K1 and in developing alternative design ideas.

Then the newly formed Royal Fine Arts Commission became involved. It had been established to advise on matters of public amenity and the Postmaster General invited the Commission to organise a further competition. A limited contest was arranged.

The Post Office and the Birmingham designs were carried forward, and three eminent architects were asked to submit further designs. The design brief recommended that the boxes should be constructed in cast iron and set a maximum unit cost of £40. Full-size models in wood of the five designs were lined up forjudging on land behind the National Gallery. The general design of Giles Gilbert Scott was favoured and, with some modifications to ease manufacture, the new kiosk was introduced in 1926. It was designated the Kiosk No. 2. It was painted 'vermilion red' outside and 'flame' inside, and weighed over a ton. It was very imposing.

Scott's classically inspired design was neat and effective. A pierced crown appeared on all four sides to provide both ventilation and a visual link with the royal crest that decorated the GPO's letter boxes. The kiosk had no unnecessary decoration and featured an elegant dome that was to become an essential element in British kiosk design for half a century. It is said that Scott was inspired by the saucer dome above the tomb of Sir John Soane in St Pancras churchyard, or perhaps by the similar lantern at the Dulwich Picture Gallery. More probably his dome qualifies as a design classic, the perfect top to a small square building that is very much taller than it is wide.