They are worth millions of pounds, and kept secure in the vaults under Buckingham Palace. They represent love, power, and intrigue. Their beauty is famed and their history is unique — one was nearly lost to a royal mistress, one was the subject of investigation, and another has links to ancient history. They are the queen's most impressive and important necklaces, and we have rounded up the top 17 in her majesty's personal collection . . .