Mistaken identity: 'You called the wrong Robert Shapiro...'
But fortunately he was still very good at answering the question.
Evan Davis had been interviewing experts about the news TV cameras can film in Crown Courts in England and Wales for the first time.
The PM programme had meant to book the famous US lawyer who helped successfully defend OJ Simpson, to discuss the development with a retired Supreme Court justice.
The interview began with a giggle.