No-one is supposed to talk about the behind-the-scenes relationship between the sovereign and the prime minister of the day.
But the Queen’s reign saw 15 premiers and inevitably snippets leaked out.
They shed light on the confidential weekly audiences that take place – usually at Buckingham Palace – about which lips are normally tightly sealed.
However, like any other individual, the Queen had her favourites among those who passed through 10 Downing Street after her accession in 1952.
She established a great rapport with Harold Wilson, Margaret Thatcher sometimes alarmed her, and she found Harold Macmillan too patrician.
Sir Winston Churchill (Conservative 1951-55)
Sir Anthony Eden (Conservative 1955-57)
Harold Macmillan (Conservative 1957-63)
Sir Alec Douglas-Home (Conservative 1963-64)
Harold Wilson (Labour 1964-70 and 1974-76)
Sir Edward Heath (Conservative 1970-74)
James Callaghan (Labour 1976-79)
Baroness Margaret Thatcher (Conservative 1979-90)
Sir John Major (Conservative 1990-97)
Tony Blair (Labour 1997-2007)
Gordon Brown (Labour 2007-2010)
David Cameron (Conservative 2010-2016)
Theresa May (Conservative 2016-2019)
Boris Johnson (Conservative 2019-2022)
Liz Truss (Conservative 2022-present)
But there seems little doubt that her all-time favourite was her first prime minister, Winston Churchill, who greeted the young, distressed woman on her sudden return to Britain from Kenya on the death of her father, King George VI.
When Churchill retired in 1955, the Queen sent him a hand-written letter telling him how much she missed him and how no successor “will ever for me be able to hold the place of my first Prime Minister to whom both my husband and I owe so much and for whose wise guidance during the early years of my reign I shall always be so profoundly grateful”.
Like a kindly uncle, Churchill had nurtured her through the early years, giving her the sort of advice which no-one else could have done.
It was something she never forgot, and she offered him a dukedom on his retirement.
Afterwards, with tears in his eyes, he said: “I very nearly accepted. I was so moved by her beauty and charm and the kindness with which she made this offer.
“But I remembered that I must die as I have always been, Winston Churchill.”
Later, he reluctantly accepted a knighthood, probably because he did not want to hurt her feelings.
He had always said he wanted no memorial “except perhaps a park for children to play in”.
The Queen’s relationship with the starchy Sir Anthony Eden was certainly more formal and she found the urbanity of Mr Macmillan not very much to her taste.
However, on one occasion, rather than discussing affairs of state at one of their audiences, the Queen and Mr Macmillan could be seen huddled over a transistor radio as US astronaut John Glenn was hurtling through space.
Unwittingly, she allowed herself to become involved in Mr Macmillan’s machinations over his successor, later described as “the biggest political misjudgment of her reign”.
But she was delighted with the outcome.
When she got the advice to call Sir Alec Douglas-Home, rather than the expected RA Butler (“not her cup of tea”), she reportedly expressed her pleasure.
An aide said: “He was an old friend. They talked about dogs and shooting together. They were both Scottish landowners, the same sort of people, like old schoolfriends.”
But it was Harold Wilson who really endeared himself to her.
“They got on like a house on fire,” one long-standing member of the Labour Party said.
He used to join members of the royal family for riverside picnics at Balmoral.
Once there, the Queen, on the spur of the moment, said to Mr Wilson: “Let’s go and see Mother.”
The pair then drove off together to visit the Queen Mother, without any detectives in attendance and with the Queen at the wheel.
However, she is said to have had difficulty in warming to Edward Heath, who always found small talk a problem.
Their weekly audiences have been described as “frosty”.
Unlike Mr Wilson, Mr Heath could not make her laugh.
James Callaghan, another Balmoral picnicker, also established a warm rapport with the Queen.
He said: “One of the great things about her is that she always seems able to see the funny side of life. All the conversations were very enjoyable.”
He added: “As prime minister you can let your hair down and there’s no-one around.
“I think after every weekly talk you come away feeling better, a bit more confident than you were before.
“In politics nowadays it helps a great deal if you have a sympathetic ear.”
But things were very different with Mrs Thatcher, who reportedly found the traditional September weekend at Balmoral painful.
One observer wrote: “A weekend in the country with aristocrats who enjoy riding, shooting, sports and games is Thatcher’s idea of torture.
“But her dread of the weekend receded as the two women became somewhat more comfortable with one another.”
Mrs Thatcher also could not abide the charades that she was expected to play after dinner at Balmoral and the Queen, at a gathering of six of her premiers, once joked about “the party games which some of you have so nobly endured at Balmoral”.
However, others have said the two women did not get on.
Another commentator said the Queen gave the impression that Mrs Thatcher was not her favourite woman.
Anthony Sampson wrote in 1982: “The relationship is the more difficult because their roles seem confused.
“The Queen’s style is more matter-of-fact and domestic while it is Mrs Thatcher (who is taller) who bears herself like a queen.”
But when Baroness Thatcher died in April 2013, the Queen took the unusual step of attending her ceremonial funeral – a personal decision and an indication of the Queen’s respect for her first – and at the time her only – female prime minister.
Some say the arrival of the genial John Major came as something of a relief to the Queen.
He was popular with the royal family, and the Queen in particular, largely because of the genuine concern he expressed for the welfare of the two young princes, William and Harry, first on the divorce of their parents and then on the death of their mother, Diana, Princess of Wales.
After Diana’s death in 1997, he was appointed a special guardian to William and Harry with responsibility for legal and administrative matters.
Diana was killed in a car crash in Paris a few months into Tony Blair’s term of office and he coined the phrase “the People’s Princess”, as well as trying to advise the royals on how to deal with the public mood.
He was described in some Palace quarters as a “head of state-in-waiting”, and there were courtiers who were not enamoured by what they saw as his encouragement of a “people’s monarchy”.
The Queen’s relationship with Mr Blair was said to have improved over the years, although it apparently lacked warmth.
Neither Mr Blair, who later revealed details of his private conversations with the Queen in his memoirs, nor Gordon Brown, who was reported to have a good but formal relationship with the royals, was invited to the Duke and Duchess of Cambridge’s wedding in 2011.
A red-faced David Cameron was forced to make a grovelling apology to the Queen in 2014 after his “purr-gate” blunder.
Mr Cameron was caught on camera telling New York Mayor Michael Bloomberg that the monarch had “purred down the line” when he telephoned and told her the result of the Scottish independence referendum.
He vowed never again to discuss his conversations with the Queen.
Theresa May was the second female prime minister of the Queen’s reign – taking up her post in July 2016 in the wake of the Brexit vote – more than a quarter of a century after Mrs Thatcher stood down.
The Queen was reported to have been disappointed when Mrs May declined to share details of her plans for leaving the European Union during her first visit to Balmoral.
Then came Boris Johnson, who succeeded Mrs May when she resigned in 2019.
Mr Johnson was only a few hours into his post when he reportedly broke protocol by revealing what was said in his audience with the Queen as he accepted her invitation to form the next Government and become PM.
A correspondent for Euronews NBC said the outspoken politician claimed the monarch quipped “I don’t know why anyone would want the job”.
Mr Johnson, who disclosed the remarks during a tour in 10 Downing Street, was told off by staff who warned him not to repeat such things so loudly.
Liz Truss became the first prime minister of the Queen’s reign to be appointed at Balmoral.
In 2022 she travelled to the Queen’s private retreat in the Scottish Highlands for the historic audience.
The monarch’s mobility issues had scuppered plans for her to make the trip to London.
Despite the lack of discretion from some politicians, if you ask anyone at Buckingham Palace about the Queen’s feelings towards her prime ministers over the last half-century, you will hear just one simple response: “We couldn’t possibly comment…”