The peace of Christmas 1940 ended suddenly and violently for Londoners on the night of December 29 when the German Luftwaffe launched an airborne attack so devastating it became known as the Second Great Fire of London. But out of the burning rubble came an image that would define the defiant 'Blitz spirit' of Britain and its capital city.

From 6.15pm until the all-clear sounded three-and-a-half hours later, some 100,000 incendiary bombs and another 24,000 high-explosive devices rained on the heart of the City, destroying many of the buildings that had stood since the City of London was rebuilt after the Great Fire of 1666.

At one point, some 1,500 fires were raging in a strip of land that stretched from St Paul's Cathedral to the borders of Islington to the north – the largest continuous area of destruction in any Blitz attack on the UK.

[Read more: November 14, 1940 - Coventry Cathedral is destroyed by German bombs]

The Square Mile in particular suffered the greatest damage. In all 31 guild halls, 19 churches (including eight built by Sir Christopher Wren) and all of Paternoster Row – the historic heart of the publishing industry – were destroyed. 160 civilians perished, along with 14 firemen, and some 500 people were injured, 250 of them fire fighters.

Amidst the smoke and flames, however, St Paul's Cathedral stood, apparently unharmed, its dome a beacon of defiance. It was no coincidence – reports suggest that Winston Churchill ordered fire fighters to abandon the City's other burning buildings and concentrate all their efforts on protecting the cathedral. They were aided by 200 or so volunteers who patrolled the church's grounds and corridors armed with water pumps and sandbags to extinguish any fires.

Just half an hour into the raid, Daily Mail photographer Herbert Mason captured the iconic image at the top of this page of St Paul's surrounded by fire. Published in his paper two days later, it is said to have given the country hope for the battle ahead and remains a symbol of Britain's indomitable 'Blitz spirit' to this day.

Also on this day: December 29, 1940 - Central Telegraph Office targeted by Luftwaffe bombers