Despite the many challenges of running a mediæval procession through modern London the Lord Mayor’s Show hasn’t been cancelled since 1852, when it made way for the Duke of Wellington’s funeral.
The Show has survived two bouts of the plague, the great fire of London, city-wide riots just before the 1830 Show and a particularly thunderous 1867 editorial in the Times which declared that "the Show will vanish but the Banquet is safe". It has moved from land to river and back again while a modern megacity grew up in the open space that once lay between the City of London and the village of Westminster.
The Show has occasionally had to adapt to its circumstances. 1915 was a recruiting Show, in which thousands of volunteers were supposed to fall in behind the Coach but were deterred by the terrible weather. In World War 2 the Show became frugal, the State Coach packed away and the pageantry replaced with a brisk military parade. Even so, at the height of the Blitz, the Lord Mayor still travelled to Westminster to pledge his loyalty to the Crown.
The route of the modern show was fixed in 1952, but still it occasionally has to be diverted around roadworks or construction. This too is nothing new. In 1676 the Court of Aldermen approved a change of route:
"The passage ... being now obstructed by the great quantities of stone laid there for the convenience of St Paul's Church."
Perhaps the biggest change in the Pageantmaster's role in recent years comes from the security requirements of a modern event. In 1761 the Prime Minister - William Pitt - took part. He was so popular at the time that the crowds mobbed his carriage and kissed his horses.
Even if the prime minister were that popular, or on a horse, the security around the modern Show makes a repetition unlikely. The policemen and women that you see on the day are the visible and friendly tip of a huge security operation that keeps both the procession and the spectators safe. Just one example: every single one one of the 3,500 manholes and 197 vacant properties on the route will have been searched and sealed before you get there on the day.