“Seeing a picture of you in today’s newspaper standing in front of a barbecue grilling quail, reminded me that I had never sent you the recipe of the drop scones which I promised you at Balmoral. I now hasten to do so,” wrote the Queen, on January 24 1960. The recipe she enclosed was for 16 people – “when there are fewer I generally put in less flour and milk” – and, as alternatives to sugar, she offered golden syrup and treacle. The mixture, she advised, ‘“shouldn’t stand about too long before cooking”.

Her correspondent was Dwight D Eisenhower, then President of the United States. Sovereign and president had met in the autumn of 1957, on the Queen’s first state visit to America, and again two years later when Eisenhower accepted a royal invitation to Balmoral. The Queen’s letter combined homeliness with informal statecraft. “A great deal of beating,” she suggested, was key to successful drop scone batter; she told the president that she had followed “with intense interest and much admiration your tremendous journey to so many countries, but feel we shall never again be able to claim that we are being made to do too much on our future tours!” 

The Queen’s letter to Eisenhower was more than recipe sharing. At heart, its ingredients were those of royal diplomacy and Her Majesty’s soft power as global statesman. Warmth and friendliness are palpable in the four handwritten sides of Buckingham Palace writing paper. The Queen expresses admiration for the then president’s recent 19-day, 11-nation tour: one globe-trotting world leader speaking to another, she is empathetic and understanding. Between writer and recipient, the letter implies, is a special relationship. It reflects in miniature the special relationship between their two countries.

For both Queen and President, today’s meeting between Elizabeth II and Joe Biden, after Friday night’s reception for the G7 leaders at the Eden Project, is a significant one. The cup of tea and Guard of Honour offered by the world’s oldest head of state to the representative of the world’s greatest superpower is a symbolic offering, token of a friendship that has been a cornerstone of British foreign policy throughout both their lifetimes.

 For the Queen, who has met every US president since the Fifties save Lyndon Johnson, the engagement is her latest service to British wellbeing on the international stage. Given the warmth of her encounters with many previous US presidents, it is almost certainly a duty she anticipates with a dash of pleasure. 

The Queen was only 16 when The Tatler and Bystander told readers, “Part – and an important part – of Princess Elizabeth’s training [for the throne] is for her to meet outstanding figures of the day.” From the outset, Americans featured prominently among these “outstanding figures”. In 1938, at the age of 12, the future queen was on hand for her parents’ reception at Windsor Castle of the new US ambassador, Joe Kennedy; four years later, Eleanor Roosevelt found time to speak to the princess alone during a wartime visit to Britain. Elizabeth, recalled the American first lady, asked her “many questions about the youth movements of America… She asked me a number of questions about life in the United States, and they were serious questions.”

1957: The Queen meets President Dwight D Eisenhower

Credit: ullstein bild via Getty Images

The Queen has remained seriously interested in Britain’s key ally. In addition to four state visits – in 1957, 1976, 1991 and 2007 – she made what the Palace described as an “official visit” to the West Coast in 1983, culminating in the dinner hosted by Ronald and Nancy Reagan at a San Francisco museum remembered chiefly for an iconic photograph of a laughing Reagan beside a deadpan monarch, the latter elaborately – even over-elaborately – dressed in champagne-coloured ruffles and bows by Hardy Amies. Unusually, given her preference for British holidays, the Queen has also made unofficial, off-duty visits to the States. In October 1984 and May 1986, she stayed in Kentucky with vice president of the American Jockey Club, William Farish, and his wife Sarah, in order to visit local stud farms.

With successive presidents and their wives, Britain’s highest-ranking diplomat has done her best to forge warm, constructive relationships. Harry Truman had anticipated a visit from George VI and Queen Elizabeth (later the Queen Mother) in 1951; the King’s poor health prevented him travelling and his elder daughter took his place. Truman did not complain. “When I was a little boy,” he reflected, “I read about a fairy princess – and there she is.” It was the smitten premier’s equivalent of Barack Obama’s heartfelt reflection on the Queen’s 90th birthday: “She is truly one of my favourite people.” 

As with prime ministers at home and across the Commonwealth, the Queen has extended to each American premier the same friendliness and lively curiosity in their national fortunes. Seventies’ Labour leader James Callaghan referred to “friendliness without friendship” in the Queen’s dealings with politicians; America’s presidents have not quibbled over the distinction. Ronald Reagan described it as a “fairytale” moment, and one of the most “fun” of his presidency; the Queen’s visit to his Santa Barbara ranch in appalling weather in 1983.

So successful was the young Queen’s charm offensive during her 1957 visit that Harold Macmillan concluded she had “buried George III [her great-great-great-great-grandfather, from whom the American colonies wrested their independence] for good and all”; and the instant rapport that Her Majesty established with the Obamas 50 years later was clear for all to see. Michelle Obama’s impulse to place her arm around the Queen at their meeting in 2009 may have broken rules of royal protocol. Clearly it did not offend the octogenarian monarch, who returned the gesture. The Queen’s dresser, Angela Kelly, afterwards described “an instant and mutual warmth… between these two remarkable women”.

1982: Welcoming the Reagans

Credit: V

In almost every instance, the Queen has also inspired admiration and respect. These are the qualities that underpin her unofficial title as her government’s “secret weapon”. Observing the Queen from a distance in the Sixties, a young Bill Clinton concluded that she was “elegant and stoic”. Thirty years later, as president, Clinton refined his view: “She’s a highly intelligent woman who knows a lot about the world… I always marvel when we meet at what a keen judge she is of human events. I think she’s a very impressive person.” 

Donald Trump’s royal encounters were fraught with protocol gaffes, including keeping the Queen waiting and walking in front of her, but his response to his royal hostess was just as wholehearted: in a speech at Buckingham Palace, he acclaimed the Queen as “a great, great woman”. Perhaps only the Duke of Edinburgh was fully privy to the Queen’s reaction to Trump’s blunders. In public, the diplomatic monarch confined herself to celebrating the two nations’ “cherished values of liberty and democracy”; her expression of bewilderment as the president walked in front of her while inspecting a Guard of Honour at Windsor Castle was scarcely perceptible.

2019: With President Trump, who described her as a 'great woman'

Credit:  Heathcliff O'Malley

Occasionally British governments have used the Queen as a negotiating tool in their dealings with their US counterparts. In the early Sixties, Britain and America were equally concerned by the possibility of Soviet influence in the newly independent west African state of Ghana. Britain’s response, despite security threats, was a high-profile 12-day royal visit to the country’s authoritarian leader Kwame Nkrumah in November 1961, following a private visit by Nkrumah to Balmoral. In its aftermath – and after photographs of a jewelled Queen dancing with a beaming Nkrumah splashed front pages globally – Macmillan told President Kennedy, “I have risked my Queen. You must risk your money.” America funded Ghana’s Volta Dam project – and Nkrumah resisted Krushschev’s blandishments.

That every living former US president issued statements of respect following the death of the Duke of Edinburgh in April reflects not only American admiration for the Queen’s late husband, but affection and esteem for the Queen herself. “Ninety-nine years old, he never slowed down at all. Which I admire the devil out of,” commented Mr Biden. His thoughts may well be remarkably similar after today’s meeting – and that will only work to the benefit of the country Her Majesty has served unflaggingly through seven decades.

The Queen by Matthew Dennison (Head of Zeus). Buy now for £19.99 at books.telegraph.co.uk or call 0844 871 1514