Bullfrog:
"So Billy Bragg's presence as a musician was to answer the question 'Michael Jackson -- bad, mad or sad?' How pathetic!!"

It was probably more to the point that he was available in case either question came up. The host (Dimbleby) is regularly at pains to point out that the guests have no pre-knowledge of the questions to be raised, but that they will be aware that the questions are likely to be about questions currently in the news.
The guest list is usually available at least one week in advance, and the Michael Jackson TV expose would not have been aired that early.

Nigel