They’re one of the most iconic and enduring symbols of London – the once ubiquitous red phone boxes. But what are their origins and how did they come to be red?

The phone boxes went through several iterations with the first standardised kiosk to house public telephones – a concrete box appropriately designated K1 – introduced by the General Post Office, manager of the telephone network, in 1921. It was usually painted cream with a red door.

The classically-styled domed kiosk known as K2 followed in 1924 after a design competition which was won by Sir Giles Gilbert Scott (the wooden prototype can still be found under the gateway entrance into the Royal Academy of the Arts in Piccadilly).

These were subsequently produced in cast iron and while Scott had apparently suggested they be painted silver with a green-blue interior, they were painted red. The Post Office’s pillar boxes were already painted this colour which was thought to be good for visibility, so it followed the colour could be used for phone boxes as well.

The K3, made of reinforced concrete and again designed by Scott, was introduced in 1929. Various other iterations were also produced including the K6 which Scott designed to commemorate the Silver Jubilee of King George VI (it was the most in-use across the UK).

New designs continued to be rolled out in the ensuing decades and appeared in a range of colours.

The number of BT-operated telephone boxes in the UK is, according to BT, said to have peaked at about 92,000 in 1992.

While many of the traditional boxes have disappeared, some have been converted for other uses – everything from mini libraries and art galleries to housing defibrillators – and BT continues to sell them, both to communities and private buyers.

While call volumes from public phone boxes have continued to decline in recent years, it was reported that about five million calls were made in the year to May, 2020, illustrating the ongoing need for some to remain.