The reader is the late Arthur Lowe. In a way, there could be no more perfect choice to impersonate Charles Pooter, the stiff late-Victorian clerk who's the supposed author of the diary, and Lowe does some things beautifully - like those primly-proud sentences in which Pooter approves the virtue of his good wife Carrie: "Gowing is sometimes very tedious and not always cautious; and Carrie once very properly reminded him that she was present."
But there is something that makes the Diary almost unsayable. It's to do with the way it overcomes a technical difficulty with the first-person comic voice. The problem is that the character must relate his own humiliations. A common solution is to make him unaware of them - as in Private Eye's "Secret Diary of John Major", where Major is always happily recording the most crashing insults to himself, through misunderstanding them. This gets tediously implausible.
The Grossmith brothers' answer is to make Pooter fully conscious of his come-uppances. He notes down all the little vanities and irritabilities which land him in them with a serene objectivity.
The result is that he becomes one of the most truly humble creations in literature, and so triumphs over all humiliation.
What tone can you find to say this in? "I was astonished." "I was disgusted." "I expressed myself pretty strongly." Such give-away words are Pooter's catchphrases. An actor, bringing the text alive, can hardly avoid vocalising them with astonishment, disgust or indignation.
But that isn't how they read. What the actor does is play Pooter at the time of the humiliation itself - for instance, when he tumbles over on the dance floor at the Mansion House Ball - not at the time of writing. Lowe is Pooter the man, yes, but not Pooter the diarist. The true comedy of the Diary lies not in Pooter's pride and falls, but in the placid candour with which he records them. It's comedy that can hardly live beyond the silence of the page.