Complex sentence: In 1695 Mordant arranged for Chaloner (still an active counterfeiter!) to address the His Majesty's Most Honourable Privy Council about corrupt practices, causing the Royal Mint to instigate its own investigations, and thus thwarting Chaloner's ambition to become its overseer.
Split into simpler sentences: In 1695 Mordant arranged for Chaloner (still an active counterfeiter!) to address His Majesty's Most Honourable Privy Council about corrupt practices. This caused the Royal Mint to instigate its own investigations, which thus thwarted Chaloner's ambition to become its overseer.