Britain's first standard kiosk, the imaginatively named Kiosk No 1 was introduced in 1912. Its design was regarded as conservative and old-fashioned.
In 1924, the Royal Fine Art Commission invited three leading architects - Sir Robert Lorimer, Sir John Burnet and Giles Gilbert Scott - to contribute designs for a national kiosk. It was stipulated that the kiosk should ideally be constructed from cast-iron with a per-unit price not exceeding £40. Sir Giles Gilbert Scott’s design was recommended and accepted and became known as the Kiosk No 2, or K2 for short. The K2 was primarily installed in London, and only a small number were ever installed outside the capital due to its cost and size.
In 1928, the GPO again commissioned Sir Giles Gilbert Scott to produce a cheaper kiosk, to be manufactured of pre-cast concrete sections. The K3 was introduced a year later in 1929.
Even as the K3 was being introduced, a new kiosk or K4, which could incorporate a stamp machine and post box; a Mini-Post Office was designed within the GPO by the Engineering Department. The decision to enlarge the K2, which was already considered too large, was curious and the whole project was quickly abandoned.
The GPO’s attempt to produce yet another low cost kiosk - the K5 - included a small number of sample models, none of which survive.
In 1935, King George V celebrated his Silver Jubilee, and to commemorate this the GPO commissioned Sir Giles Gilbert Scott to design a new kiosk. His latest design drew clear influences from the K2, but was smaller and, more importantly, cheaper to produce.
With the K6 or Jubilee Kiosk, the GPO actively sought to install kiosks more widely. To that end, they established a number of schemes, starting with the Jubilee Concession, which sought to make a kiosk available in all towns and cities with a Post Office.
Some 60,000 examples were installed across Britain, which is why the K6 has come to represent the red Telephone Box. Over 11,000 K6s remain and they are the most visible examples of the eight kiosk types that were eventually designed.
Of the 12 kiosks in Gibraltar, ten are K6 type kiosks and two are of the larger K2 variety.