“He had just been unloading meat carcasses. And he said at the top of his voice, ‘someone told me JK Rowling was in here’ and he looked directly at me.
“And he then went, ‘I wouldn’t know what she looks like’ and walked out again.
“I just froze… we both just looked at each other and that was that.”
She also told Norton she used the male pen name for her contemporary crime novels about a unconventional private investigator because she “wanted not to be me”.
“I’d always wanted to write crime and I wanted to not do it with any fanfare,” she added.
“So I submitted the manuscript anonymously, and it was all great and I even enjoyed getting rejection letters again. It was fantastic, it was just like it used to be.”
She said she “did get away with it up to a point”, and she had wanted to get three of the books out “without being unmasked”.
“Because then I thought it would have a bit of momentum. I was a bit unlucky the way it happened.”
Rowling’s identity as the real writer of the novel was unveiled five years ago when a member of an entertainment law firm told his wife’s best friend, who then shared the news on Twitter.