Possible Clues:

• This, perhaps, will never be nonplussed
• More of those books published at the same time, by the sound of it
• That's more like a tot
• Never M in us for this - only more so
• Blessed event
• A sum
• That won't make one 15 across
• And anyhow the silly idiot put in for more
• Reckoning I did not go off key, for a start
• Simple arithmetic