Possible Clues:

• Possibly perceived perusing poetry, perhaps?
• Repeated first letters
• Nothing but repetition? Rather regular repetition, perhaps
• A feature of double dosing doing everything with repetition
• What 17-, 33-, 47- and 66-Across exhibit, despite appearances to the contrary
• Peter practised poetic ploy perfectly
• Initial repetition is only repetition after all
• What William Wordsworth wrote, perhaps