"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