It’s June 2008. Boris Johnson is the newly elected mayor of London, and he has been invited to Clarence House to meet the then Prince of Wales. He and his communications director, Guto Harri, take the Jubilee Line on the Underground. Unfortunately they take a train going in the wrong direction. When they get to Canary Wharf, three stops later, they realise their mistake, jump out of the train and get back on one heading into central London. They are going to be late.

“We ran from Green Park to Clarence House,” recalled Harri, “both of us slightly panting, me a bit stressed at this point. Then it was, ‘How do we get in here?’ He said, ‘Don’t you know?’ I said, ‘No, I assumed you knew.’” They ask the soldier standing guard outside, but he remains silent. Harri says, “For f***’s sake, he is the mayor of London, he’s late to see the future King, can you just give us some idea?”

The soldier casts his eyes to one side, they follow his gaze and finally work out how to enter. Inside the first person they see is Manon Williams, one of Charles’s private secretaries (and Ffion Hague’s sister), who says to Harri in Welsh, “Paid â becso, ma’ fe’n iawn” — “Don’t worry, it’s all fine.” “What?” says Johnson. “We were at school together,” Harri explains; a Welsh-language state secondary school in south Wales. Johnson replies: “Crikey, I expect to meet someone I’ve been to school with at a royal palace, not someone you’ve been to school with.”

Boris Johnson and the Duchess of Cornwall at Clarence House.

Queen Camilla with Boris Johnson in 2010

DAVID CRUMP – WPA POOL/GETTY IMAGES

Exactly what happened when Johnson was finally ushered into the royal presence is not clear. The meeting did not go badly, but Harri got the impression that “there was not a lot of warmth there”. Charles, he felt, had taken “just a tiny bit of offence” at Johnson being late. “There was never a lot of love for [Boris].”

Johnson got on a lot better with the Duchess of Cornwall, who had a remarkably frank conversation with him in his early days as mayor. Some months after his first unfortunate audience with Prince Charles, Johnson was invited to Clarence House to meet Camilla. She had apparently told Charles, “He looks like such fun. Can we have him over for tea?” This time there was no risking the Tube; he and Harri cycled from City Hall. They were parking their bikes in the shed at the back of Clarence House when the duchess appeared, saying, “Oh, I didn’t believe them when they said you had cycled!” Harri recalled: “She had come out to the bike shed to see us. We drop the bikes, she grabs him by the wrist and says, ‘You and me, upstairs — now!’”

Camilla Shand and her mother in 1965.

Queen Camilla with her mother, Rosalind Shand, in 1965

DESMOND O’NEILL FEATURE

After an hour Johnson reappeared. “Boris was raving about her,” Harri said. “They obviously got on like a house on fire. He was making guttural noises about how much he admired and liked her. But the serious conversation they had was about her being the victim of an attempted sexual assault when she was a schoolgirl. She was on a train going to Paddington — she was about 16, 17 — and some guy was moving his hand further and further …” At that point Johnson had asked what happened next. She replied: “I did what my mother taught me to. I took off my shoe and whacked him in the nuts with the heel.” Harri said: “She was self-possessed enough when they arrived at Paddington to jump off the train, find a guy in uniform and say, ‘That man just attacked me’, and he was arrested.”

The relevance of this conversation was that Johnson at the time wanted to open three rape crisis centres. There was already one in south London, and he wanted to open ones in east, west and north London. Harri said: “I think she formally opened two out of three of them. Nobody asked why the interest, why the commitment. But that’s what it went back to.”

Power and the Palace by Valentine Low (Headline Publishing Group £25). To order a copy go to timesbookshop.co.uk. Free UK standard P&P on orders over £25. Special discount available for Times+ members.