“A portrait of loneliness” is how Cate Blanchett describes Richard Eyre’s spiky adaptation of Zoe Heller’s novel. Spot on, that, and Eyre concurs in his detailed, albeit dry chat-track, revealing that the opening shot alone is designed to amplify the “long-haul solitude” of Judi Dench’s character. Dame Dench is history teacher Barbara Covett, a fag-end-of-life failure whose diary entries spit’n’hiss when she finds new teacher Sheba (Blanchett) giving a pupil a blow-job. Her jealousy of Sheba’s looks and class turns into blackmail and odd delusions of friendship. Patrick Marber’s script crackles when it comes to collisions of private life with public view. You’re left feeling soiled but grubbily gripped, like you are actually reading someone’s diary.