williamseal, "i" is an abbreviation for "indeed". The final definition in the BRB is "aye", qv and you will see "indeed" as one of the meanings.
As for difficulty, I think Kea is the most consistently excellent Listener setter, and I thought this was fabulous. It's the type of puzzle which feels borderline unfair until one solves it, when relief and admiration combine to make one feel it was probably just about ok.
It is true, of course, that there is a good deal of more or less cold solving required before one can start to guess at the message, which helps a great deal.
But I do have to disagree strongly that the puzzle was too difficult. Very challenging, certainly. But if all puzzles were set at a level where solvers of all levels of ability and experience could complete them without help, they would be of little interest to those who require and expect a serious workout. This is supposed to be the premier thematic crossword, after all. My own view is that the puzzle has been dumbed down significantly in recent years. An occasional one like this, like an occasional numerical, ought to be fair enough. If we lose puzzles like this I for one will stop bothering.
I note that you were not complaining, and from your previous posts I've always found you very fair-minded, so I hope you won't mind my two-penn'orth.