Former editors of The Age have rubbished Gina Rinehart's provocative claim that Fairfax chairman Roger Corbett and his predecessor Ron Walker overrode the paper's charter of editorial independence by instructing an editor how to do his job.

The mining billionaire made the allegation in her Friday open letter to Corbett in which she told the ex-Woolies boss to resign unless he lifted the company's share price by 60% by November. In the scathing letter, Rinehart accuses Corbett of hypocrisy for denying her seats on the board on the grounds that she has refused to comply with the editorial charter: