Possible Clues:

• Crucially influential
• Influential discussion group with U-turn at the end?
• Ground-breaking railway shunned by academy adjoining line
• Mike, in breaking lock, shows key
• Groundbreaking symposium given a change of direction
• Groundbreaking, in a way
• Highly original
• Creative Tracey, entering limited auction, is influential
• Ground-breaking tutorial cut short by head of Latin
• Very important if dropped from cup tie?