And then there was the case of the Hong Kong Economic and Trade Office’s “bun tower” getting stuck under Chelsea bridge in 2006. Based on a traditional tower, usually made from bamboo and covered in baked buns, a steel replica was create in Wales and a driver was given “very detailed instructions” on how to get it into London the night before the show. “Of course, it came in on the Friday night, the bloke driving it ignored all the instructions and put the directions in his sat nav and ended up wedging it under the bridge in Chelsea,” Mr Reid said.”This bloody thing just wedged itself completely under the bridge and London traffic came to a standstill until somebody went and let the tyres down and got it out, it was extraordinary.” Mr Reid said he usually spends around 15 months planning before the big day “You are dealing with lots of complex relationships, people who want to be in a certain place, for example Hong Kong has a particular number they like because it is luckier than any other number so we try and build that into [the procession].”While dealing with each organisation’s request, he also has to make sure the bands are far enough apart not to drown each other out and animals that “don’t like other types of animals” are separated.”You can’t mix donkeys and horses, you can’t mix reindeer and horses so you have to have them in different places and they don’t like it if they smell each other,” he said. “It is bonkers really, the whole thing. It takes a good bit of fiddling with.”The Wednesday before the parade each year the organisers run what has become known as a “ghost parade”, wheeling the Lord Mayor’s carriage out in the early hours. The new Lord Mayor, Dr Andrew Parmley, and his wife Wendy wave from the coach during the rehearsalCredit:Dominic Lipinski/PA Wire It is the perfect parade; a three-mile procession steeped in 800 years of tradition and watched by hundreds and thousands of people as colourful floats, marching bands and, finally, the Lord Mayor’s golden carriage pass through the streets of London. But behind the scenes of the Lord Mayor’s Show is “organised chaos on a colossal scale” with last-minute mishaps and unexpected issues forever cropping up, the show’s pageantmaster has revealed. In a rare interview, Dominic Reid, an architect and solider who is celebrating his 25th year organising the parade, revealed the secrets of getting the world’s largest unrehearsed procession to run smoothly. This year, the show will welcome the new Lord Mayor Dr Andrew Parmley, the principal of the private Harrodian School in Barnes and organist of 35 years at St James Garlickhythe church. It will have a particular emphasis on music, including a special commission. Mr Reid, who is also the managing director of the Invictus Games Foundation and who took over the pageantmaster role from his father John, said he “loves” organising the show and has no plans to retire, as yet. “We have had lots of fun along the way, it has been a fantastic privilege to do it,” he said. “It has been really wonderful and my life now populated with these daft and insane moments.”The Lord Mayor’s Show is on Saturday. It starts at 9am with a river pageant before the procession, which starts at Mansion House, at 11am. The fireworks are at 5.15pm. The Lord Mayor of London’s State Coach passes St Paul’s Cathedral during the rehearsal for the show on Wednesday Credit:Dominic Lipinski/PA Wire The Hong Kong Economic and Trade Office’s “bun tower” got stuck under Chelsea bridge while being transported to the show in 2006 Despite the rehearsal happening annually, Mr Reid said Londoners still haven’t caught on. “What I love are the people who just encounter it on their way to work and look absolutely amazed… it is entertaining,” he said. But despite the careful planning, there are always things that go wrong. “There is always something, I remember once turning up and somebody had very carefully built a traffic island somewhere where I wasn’t expecting to have a traffic island,” Mr Reid said. “It stopped us getting from one side of the road to the other and caused us to reroute a whole lot of stuff.”In 1994, Mr Reid forgot to make sure Christopher Walford was in the back of the Lord Mayor’s carriage before it set off.Eight years later, the then Lord Mayor, Roger Gifford, had to be transferred into the back of Mr Reid’s Land Rover mid-parade when one of the wheels on his carriage “jammed on” at Blackfriars.”He was very humourous about it and it all went down very well,” Mr Reid laughed. Speaking to The Telegraph ahead of this year’s show on Saturday, the 55-year-old said he usually spends around 15 months planning before the big day. It takes him up to three days to decide on the running order of the procession alone – a process he calls “shunting” – as he uses colour-coded cards to ensure he meets each float, charity, band and organisation’s specific needs. He not only meticulously measures the route, calculating timings to the nearest second, but “walks it a lot” including at 4am just to check nothing has changed. “I have a very complex spreadsheet with an algorithm built into it that helps me calculate timing and gaps and stuff, but the actual putting into order we do with cards and slots on a board,” he said. The steel replica eventually made it to the show Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.