AMID all the daunting challenges of Brexit, Boris Johnson is preparing himself for one more; his first visit as Prime Minister to Balmoral.

A summer trip to see the Queen on Royal Deeside has become a regular feature of the prime ministerial calendar; time perhaps to discuss governmental matters with Her Majesty, and others, in a less formal atmosphere.

But, of course, the setting is still grand, a castle not a palace, and the company is the head of state and members of the Royal Household. Formality is never far away.

The PM - the 14th to be hosted by the Queen at Balmoral - is not due to travel to Aberdeenshire this weekend and the following one he will be in Biarritz for his first G7 summit. So, it is expected Mr Johnson will venture northwards in early September, possibly on the first weekend before MPs return to Westminster from their summer break and resume the tortuous process of ensuring Britain leaves the EU – or not – on October 31.

A question-mark has been raised as to whether Mr Johnson, 55, will take to Balmoral his partner, Carrie Symonds, 31, who has now, it is believed, moved into his 11 Downing St flat.

It has been suggested Her Majesty still observes the rule instigated by Queen Victoria that unmarried couples are not hosted overnight.

At Christmas in 2017, the then engaged Prince Harry and Meghan Markle were invited for lunch at Sandringham, the Queen’s home in Norfolk, but rather than staying overnight there, they ended up sleeping at the nearby home of the Duke and Duchess of Cambridge. A year later, the newly married Duke and Duchess of Sussex were allowed to sleep over at Sandringham.

The PM has not yet finalised his divorce with his estranged wife Marina Wheeler and so, if he is accompanied by Ms Symonds, royal protocol means it is unlikely they will spend the night in one of Balmoral’s 52 bedrooms.

Mr Johnson’s two predecessors – David Cameron and Theresa May – stayed overnight at the castle with their spouses.

In his memoirs, Tony Blair gave a sense of what a prime ministerial visit to Balmoral was like, writing candidly about his and his wife Cherie’s “freaky” stays there.

Mrs Blair claimed she and the then PM conceived their son Leo while staying in the Queen’s castle in 1991. It came about because the couple were trying to stay warm in the chilly Scottish climate and she had forgotten to pack her “contraceptive equipment”.

When Mrs Blair invited the Princess Royal to call her Cherie, Anne frostily replied: “Actually, I prefer Mrs Blair.”