Possible Clues:

• Part of play I call upon without one forceful person
• One who plays a vigorous role, especially in politics
• One with a cause
• Human dynamo is in Berlin following late part of play
• Militant to work on arranged visit
• Militant is seen interrupting penultimate and last parts of 'Hamlet'
• Party worker to behave during lively visit? On the contrary
• Political type might stop by and behave badly
• Militant to take steps on arranged visit
• Campaigner, one in set, is occupying seat of Australian government