Possible Clues:

• Unreasonable demand from high rank
• Demanding work, as the building of Babel was?
• Story about aristocrat meeting king's unreasonable request
• Challenge High Command
• Tough challenge
• That's the height of unreason
• A lot to ask about funny Cockney's titfer, seen back to front
• Big undertaking
• Difficult assignment given by high command
• Difficult instruction