Peter Ackroyd, the biography

Who is Tim Martin? What is he trying to hide? Why does he spend an entire interview with Peter Ackroyd effacing himself?

"He [Ackroyd] orders a glass of wine. A bottle is proposed. Yes! he says eagerly."

Was the bottle proposed by a third person? Did someone shout over Tim Martin's shoulder as he or she was passing? I think we should be told.