It is an initiation ceremony unlike any other.
Princess Diana is said to have passed it with flying colours but Cherie Blair is reported to have failed after causing offence by, among other things, her choice of clothes.
Now the hospitality offered by the Queen to visitors at Balmoral Castle is set to come under the spotlight in the new series of The Crown.
Episode four of the hit drama’s latest season – which launches next month – is titled The Balmoral Test.
The “test” is the name given to the royal scrutiny guests to the Queen’s Aberdeenshire home believe they are under when invited to join her on her annual break at Balmoral.
Former royal butler Grant Harrold worked for the Royal Family for seven years and met many guests of the Queen.
Grant, 42, who grew up in Airdrie and has worked for Prince Charles, Camilla, Prince William, Kate and Prince Harry, said: “Balmoral, like Sandringham, is the Queen’s private family home.
“If she invites you to Balmoral, then you are being invited to spend time with the Royal Family in a personal setting.
“You are going to be dining with the Queen – lunch, dinner, perhaps a picnic or even a barbecue.
“You are going to be out on the hills with the Queen or other members of the Royal Family, perhaps fishing, hunting or doing other country pursuits.
“Balmoral is a great place to be around the Royal Family and for them to get to know you.
“It can be a bit of a test to make sure you pass the muster.
“You are going to want to dress the part, speak the part and behave the part.
“For Princess Diana, that was easy. She came from a similar background but that’s not true of all the
guests who are invited to Balmoral.
“It can be terrifying for anyone to spend a few days with the people who are going to be your in-laws regardless of who they are, let alone one of them being the Queen”
Episode four of the new Netflix series is dedicated to former prime minister Margaret Thatcher’s failure to master royal protocol.
The Iron Lady, played by actress Gillian Anderson, had a complicated and often tense relationship with the monarch.
She is said to have viewed early visits to Balmoral as comparable to “purgatory”.
The episode also features the first visit by Princess Diana to stay with the Royal Family at Balmoral. Unlike Thatcher, Diana, played in The Crown by Emma Corin, had grown up mixing in royal circles – her peer father served as an equerry to both the Queen and king George VI.
But Grant said the Monarch always goes out of her way to make everyone invited to stay at Balmoral feel welcome.
He said: “I started working for Prince Charles in 2004 and a couple of days later was sent to Scotland so my introduction to the royal household was at Balmoral – at Birkhall. That was my Balmoral test.
“It was nerve-wracking even for me as a member of staff because you are around the royals there all the time, even when off duty – and can bump into them anywhere.
“I was off one afternoon and was on a horse out in the hills and my horse started to react to something at its feet.
“I realised it was a corgi and looked up to see the Queen, complete with headscarf.
“I just said, ‘Good afternoon, Ma’am,’ and she wished me a good afternoon, then off she disappeared.
“Not long later I was at the Ghillie’s ball and danced with the Duchess of Cornwall, before then finding myself dancing a reel alongside Prince Charles and the Duke of Edinburgh, and doing a jig with the Queen. That’s Balmoral for you.
“The Queen is not someone who likes to put people on the spot. She always wants her guests to relax and be comfortable.
“What makes an invitation to Balmoral so special is that, unlike Buckingham Palace or Windsor Castle, it’s a private residence.”
Grant, who runs his own company offering etiquette courses, said his advice for those invited as a guest of the Queen is always the same.
He added: “Find out what you need to bring, know the dress code – don’t turn up with pink fluffy wellies when everyone else will be wearing Hunters – and know the social etiquette.
"Be on time – never keep the Queen waiting. Follow the lead of the Royal Family and always be nice to the dogs.”
