For the first time in her 70-year reign, Her Majesty may opt to break tradition. Photo / Getty Images
The Queen could travel to Trooping the Colour in a Range Rover instead of a royal carriage for the first time in her 70-year reign under contingency plans being drawn up by officials.
The 96-year-old monarch may end up making the journey from Buckingham Palace to Horse Guards Parade by 4x4 - with a full Sovereign's Escort of Household Cavalry.
It is one of several "Plan Bs" under consideration for the Platinum Jubilee weekend after palace sources suggested Her Majesty's attendance at events marking her historic milestone would not be confirmed until the day in question.
On Monday night, Buckingham Palace distanced itself from speculation that the Queen would not appear on a dais to inspect the troops - but instead watch her official birthday parade from the Major-General's office, also known as "Wellington's office", which overlooks the parade ground.
Pointing out that the Queen sat on a dais for last year's ceremony of pomp and pageantry at Windsor Castle, a royal insider said: "I cannot imagine in 100 years that if attending, Her Majesty wouldn't be seated on a dais in Horse Guards Parade.
"All the plans are fluid at the moment and nothing has been finalised."
The Household Cavalry is understood to have been briefed on some of the different options in light of the Queen's recent mobility problems.
She has been forced to cancel a string of engagements since pulling out of the Remembrance Service at the Cenotaph last November after straining her back.
In February, she met with Major General Eldon Millar, Defence Services Secretary, and his predecessor Rear Admiral James Macleod at Windsor Castle and joked as she shuffled towards them carrying a walking stick: "Well, as you can see, I can't move."
The "Range Rover plan" would see four mounted divisions escort the Queen's car up The Mall to the event on June 2, while other members of the Royal family would stick to the tradition of travelling there by carriage.
As the "Royal Colonels", The Prince of Wales, the Duke of Cambridge and the Princess Royal are expected to take part in the ceremony on horseback.
A well-placed source told the Telegraph: "The Range Rover plan is a departure but it is not unprecedented for the Queen to have an escort of mounted troops when she is travelling by car. It has happened in the past on foreign visits.
"The reason for the change is both speed and comfort. It is no longer comfortable for the Queen to travel by carriage or to be standing on a dais for an extended period.
"After the Derby, of all things she's doing over the Platinum Jubilee weekend, she's most looking forward to this.
"The Queen always takes a close personal interest in the parade, which is essentially her guards' birthday present to her, and this year will be no different. HM has been known to be able to spot an upside-down button at 100 paces in the past."
The Queen's aides have spent weeks working on the plan with HQ London District, the army base responsible for all London's ceremonial events.
While the final arrangements for the extended bank holiday weekend are still being finalised, it is understood Prince William will be taking the lead on military events by reviewing the Trooping the Colour in a formal inspection the week before the parade.
It is not yet known whether the Duke and Duchess of Sussex will be attending any of the festivities amid an ongoing row over their security in the UK.
Prince Harry is suing the Home Office after being stripped of his taxpayer-funded Metropolitan Police protection officers, claiming it is no longer safe for his family to visit Britain without them.
The couple has reportedly received reassurance that they will be protected by a Special Escort Group (SEG) detail if they attend the celebrations with their son Archie, two, and 10-month old daughter Lilibet, who the Queen has not yet met. It comes after they paid a private visit to the Queen at Windsor Castle on April 14 en route to the Invictus Games in the Netherlands.
Flypast and 41-gun salute
Trooping the Colour has marked the official birthday of the British sovereign since 1748 and recreates the march of a regiment's colours, or flags, on the battlefield.
After the royal procession to Horse Guards Parade, the Queen receives a royal salute and inspects her troops of the Household Division – both foot guards and horse guards – and the King's Troop, Royal Horse Artillery.
Each year, one of the foot-guards regiments is selected to troop its colour through the ranks of guards. Then the entire Household Division assembly conducts a march past the Queen, who is saluted from the saluting base.
Returning to Buckingham Palace, the Queen watches a further march past from outside the gates. Following a 41-gun salute by the King's Troop in Green Park, she leads the Royal family on to the palace balcony for a Royal Air Force flypast.