They have protected Prime Ministers, foreign diplomats and heads of state; and whenever the Queen leaves Buckingham Palace they escort her on her journeys through London.
They worked closely with Princess Diana and their next job will be to escort and provide security and protection for her son Prince Harry and his bride Meghan Markle when they marry at Windsor on May 19.
Until now the exploits and adventures of the Metropolitan Police's Special Escort Group have been largely unheralded and unpublicised.
But a new book, Escorting the Monarch, by Chris Jagger, a former intelligence officer who worked with Britain's Special Forces, reveals for the first time details of the SEG's work and gives a unique insight into what goes on behind-the-scenes.
Jagger, who spent 20 years in the intelligence community, much of the time tackling organised crime in the Balkans says: "The SEG will play an important part in the security of the coming Royal Wedding and it will be a huge security operation.
"The biggest challenge for the officers involved ---and there will be many--- is to not be seen. No one wants the wedding to be dominated by an atmosphere of security. Nonetheless, the assumption made by those in command of security will be that all measures will need to be in place. Planning is well underway.
"The SEG will have various roles during the wedding, one of which will be to ferry our own VIP's and Heads of State to and from the proceedings."
His book gives a detailed account of the group's history---it was formed in 1952 to escort Yugoslav Prime Minister Marshal Tito who was believed to be in danger of an assassination attempt---and how it evolved in response to changing and ever more dangerous times.
As well as escorting kings, queens, presidents and emperors, the 35-man group has escorted priceless works of art, gold from the Bank of England, terrorists and high-risk Category A prisoners.
"The group are unlike any other," he says. "They prefer the low-key approach, and aim for elegance rather than presence. This is for several reasons - partly due to the complexity of navigating London's traffic, partly because they firmly believe it is the safest and most secure way, but mostly because Her Majesty and Prince Philip insist on keeping a low-profile, and not disrupting the flow of London. Neither of them like the noise, fuss and aggression that comes with conventional security convoys."
The book has a website, www.escortingthemonarch.com and a Facebook page https://www.facebook.com/