Mr Lewis pointed to how the book, which is being serialised in the Daily Mail, contains some “remarkable” details about the late Queen’s final days and Charles’s first days on the throne.
“It actually includes the note that the late Queen’s private secretary Edward Young wrote about her final hours,” he said.
“I think it’s actually very moving, that passage in particular. But from my experience, it’s pretty unusual because there is something called the 20-year rule and most of the stuff that goes on in and around the institutions of the UK is covered by that.”
However, Mr Lewis said: “I can completely understand why the King’s men have done it. They’ve given Robert Hardman unprecedented access but they know him very well, he’s got a track record.
“I think it’s a practical change of strategy. They haven’t given away any official secrets but here’s the interesting thing – it’s let us all in a bit closer to what frankly was a series of truly historic events.”
Mr Yelland described it as the “correct PR strategy”, adding: “It has not really been dwelt on probably by anyone else. It’s a big move it’s important.”
