Possible Clues:

• Crime first off with purpose creates basis for discussion
• It's much discussed
• Following topless Dot is a topic of conversation
• Little thanks to second-class member of royal family with Spike - that's a topic of conversation!
• Position after chess player has taken piece is a matter for debate
• 1 down could be irritated by this subject for discussion
• Topic inviting discussion
• Matter of discussion
• Subject of monarch protected by it - plan to be devised