Possible Clues:

• Support for spur round horse's middle
• It interrupts humming noises around bit of ear
• Republican brought in to agitate gets a foothold
• Old Labour supporter to cause trouble taking on Right
• The jockey always puts his foot in it!
• Rider's footrest
• Ultimately ear piercing to arouse a tiny part of the ear?
• Small bone of the middle ear — it purrs (anag)
• Agitate about right sort of cup
• Bone, radius, found in fire