Possible Clues:

• Premier having drink with army engineers
• Crowning the young Diana R.?
• Highest rising American with power over British engineers
• Wrongly presume it's similar to 27 down
• The best drink regularly tried by this writer
• Sovereign to dine with army unit
• *Unparalleled
• Greatest in status, authority or power
• Chief beginning to size up British Army corps
• Presume novel of highest status