U.S. President Donald Trump is slated to pay a state visit to the UK in October, and the Times of London has reported that the American chief executive has “demanded” a “gold-plated carriage” journey down The Mall to Buckingham Palace with Queen Elizabeth II after he arrives in London:

Donald Trump waving from the Queen’s royal carriage is not a scenario many would have foreseen a year ago, but it has become a very real prospect, forcing security services to plan an unprecedented lockdown. The White House has made clear it regards the carriage procession down the Mall as an essential element of the itinerary for the visit currently planned for the second week of October, according to officials. Security sources have warned, however, that the procession will require a “monster” security operation, far greater than for any recent state visit.

This mode of travel isn’t so unusual, as taking a carriage ride along the Mall from the Royal Mews to Buckingham Palace with the Queen is something of a tradition for world leaders. When Mexican president Enrique Peña Nieto undertook his first state visit to Britain in 2015, for example, he rode with the monarch to Buckingham Palace:

Prince Charles and his wife, the duchess of Cornwall, went to pick up Peña Nieto and Rivera at a downtown London hotel where they stayed their first night in the British capital before beginning their state visit. The queen was waiting for them at Horse Guards Parade in Whitehall and shook hands with the Mexican head of state before introducing him to Cameron and other government officials, including Deputy Prime Minister Nick Clegg and Home Secretary Theresa May. After the formal ceremony, the Mexican president accompanied the queen in her carriage to Buckingham Palace, where they had a private lunch and afterwards had a look at some Mexican works in the Royal Collection. Peña Nieto and Rivera later visited Westminster Abbey, where they placed a tribute on the tomb of the unknown soldier.

Russian President Vladimir Putin and Chinese President Xi Jinping have also taken such carriage rides during state visits, although U.S. President Barack Obama eschewed the tradition in order to avoid the elaborate security precautions it would require. A source quoted by the Times described the security drawbacks of the traditional carriage as follows:

“The vehicle which carries the president of the United States is a spectacular vehicle. It is designed to withstand a massive attack like a low-level rocket grenade. If he’s in that vehicle he is incredibly well protected and on top of that it can travel at enormous speed. If he is in a golden coach being dragged up the Mall by a couple of horses, the risk factor is dramatically increased.” “There may well be protections in that coach such as bulletproof glass, but they are limited. In particular it is very flimsy. It would not be able to put up much resistance in the face of a rocket propelled grenade or high-powered ammunition. Armor-piercing rounds would make a very bad show of things.”

The White House has not returned our request for comment on the subject.