“Hey, I know you!” exclaims Paul McCartney, gripping my hand as we walk into his office in central London.

I’m instantly disarmed. All my nerves evaporate. And while I’m realistic enough to know he doesn’t really hold treasured memories of our previous encounters, I’m impressed by his ability to defuse the tension of Meeting A Beatle.

We gather in Soho at lunchtime. Instead of Wild Honey Pie or Savoy Truffle, McCartney has opted for a simple bagel (topping: a terrifying blend of Marmite and hummus), which he prepared in a kitchenette next to his assistant’s desk.

As he eats, he scans a printed list of film titles – mainly vintage comedies – looking for something to play at his family movie night.

“It’s hard to find something I haven’t seen,” he laments.

Lunch finished, we settle next to a Wurlitzer jukebox in the corner of the room. McCartney places his phone face down on the table – revealing a case printed with a colourful holiday photo.

“Is that the family?” I ask.

“Yeah, that’s my grandkids. Four of Stella’s and four of Mary’s.”

“They’re all very bright,” he beams, pointing to each one in turn and listing their Ivy League achievements. “Yale, Brown, Brown, NYU, Yale again.”

“Are you an indulgent granddad?”

“Yeppp!” he confirms. “They’re very lovely. I love them.”