US President Donald Trump is expected to adopt a softer tone than the one he set earlier this week at a NATO summit when he takes tea with Britain’s Queen Elizabeth II.

Mr Trump and his wife Melania are due to meet the 92-year-old monarch at Windsor Castle on Friday afternoon (local time), and the imposing setting and the Queen being one of the most admired women in the world are expected to temper the President’s iconoclastic ways.

The Queen has met every US president since Dwight Eisenhower – except Lyndon Johnson, who did not visit Britain while in office.

There are rules of etiquette for encounters with the monarch, although they are less rigid than many believe.
 Chief among them: Don’t get too affectionate with the Queen, who does not expect to be hugged or kissed by guests.

Paul Keating was famously dubbed “the lizard of Oz” for putting his arm around the Queen in 1992. Photo: ABC

Etiquette will require the Trumps to wait until the Queen offers her hand, then to shake it politely and move on.

Neither will be likely to bow or curtsey when they meet the Queen, said Hugo Vickers, an author who has long chronicled the British royals.

“That wouldn’t be required from a head of state or the wife of a head of state,” he told The Associated Press.

“He would be wise not to attempt to kiss her, and I don’t expect for a moment that he will.”

Throughout their meeting, deference is expected to the monarch: Arrive before her, don’t speak unless spoken to or sit or eat until she has, and never turn your back on the Queen or leave before she does.

Mr Trump has told British tabloid The Sun that he’s not nervous about meeting the Queen, who he called “a tremendous woman”.

“I really look forward to meeting her. I think she represents her country so well,” he said.

Michelle Obama also got touchy with the monarch. Photo: AAP

Buckingham Palace has called the get-together at Windsor Castle a “working visit” (i.e. not an official state visit.). That means no speech to the British Parliament for Mr Trump, and no state banquet.

Mr and Mrs Trump will be greeted at Windsor by a royal salute from a guard of honour, and the playing of the US national anthem.

Upon actually meeting the Queen, the Trumps will be expected to call her “Your Majesty”, and then “Ma’am” (to rhyme with “jam”).

But the Queen wasn’t upset when South African president Nelson Mandela called her Elizabeth. Nor was she miffed when Michelle Obama briefly put her arm around her.

The Queen, who is the longest reigning monarch in British history, has shown herself to be unflappable when the unexpected occurs.

She is not known to show anger in public – and the only times most people have seen her show unbridled glee is when one of her racehorses performs extremely well in a competition.

-with agencies