It didn't take me all that long to fill the grid with the entries and then fill the gaps to form the last three words of the 'description'. However, I then spent almost an hour trying to fully parse a few clues in order to determine the extra letter and get a coherent full description. I didn't want to trust to luck because Schadenfreude is known for setting traps in his endgames, and I suspected the highlighting might not be as straightforward as it appeared. 2d was one of that handful of clues, and since I had an alternative, perfectly justifiable extra letter for 45a I had what appeared to be nonsense in the middle of the description.
I'm inclined to agree with Ruthrobin that the 'nut' reference was a bit unfair in the context of a clue with extra letters in the wordplay (a gimmick that is become terribly over-used in the Listener). The clue also leads to a completely different, fully justified answer, so that added some ambiguity. Another ambiguity was in 38d, where an alternative spelling of the answer was justified. Normally the Listener advises setters against this.
It all came right in the end, and it was nice to end up with real words and no ambiguities.