Uncle DaveO you've got a good test, and for people who don't know the answer instinctively it can also be used to resolve the I/me question. BUT.... You've allowed Amos to lure you away from the phrase at issue. It is depending on who, not write for who. I wonder if Amos would ever write depending on whom you ask. For my money Mrs Beezley was right and deserves to have her PC returned.

Notwithstanding his pontificating on the subject, George Orwell had a ponderous, sometimes laboured style. However he did write (in a different essay) "The art of writing lies largely in the perversion of words." He was bemoaning gaps in even in the colossal English-language vocabulary and must have had a point or Edith Sitwell would not have needed to write: "The morning light creaks down again."

A well-known British author Alan Sillitoe has always tested the quality of his writing by seeing how it sounds when he reads it aloud.

Rapaire, there is nothing exceptional about it's and its. One is a contraction, the other is a personal adjective like his. Or should that be hi's?