Katharine Hepburn was as strong-willed and prickly as the characters she played, previously unreleased diaries and private letters have revealed.

The papers, covering her theatre career and donated by the trustees of her estate to the New York Public Library for the Performing Arts, show the late actress as the sort of woman prepared to call a policeman a "moron" to his face and to fight for the right to utter expletives on stage.

The 22 boxes of papers, which include scripts, photographs, letters and scrapbooks, also show that Hepburn was insecure about her acting, especially on stage. She made pages of notes on intonation, cadence and pitch for a voice that Tallulah Bankhead once compared to "nickels dropping in a slot machine".

Hepburn, who died in 2003, threw away very little, providing much for acting scholars and fans to pore over once the papers go on public display next February after they have been catalogued.

On a 1950 tour of As You Like It Hepburn records in her journal how she was arrested for speeding by an Oklahoma policeman.

Taken to a local lawyer's office, she slammed the door in the officer's face as she announced: "I have been arrested by this moron."