Barbara Covett (Judi Dench) - note that grasping surname - is not a popular figure at the North London comprehensive where she teaches history. To the staff and the students she is, in her own words, ‘a battleaxe’, and to the headmaster, she is an obstacle to reform. Living alone in a cramped flat, she confides to her diary her feelings of despair and loneliness. Enter the new art teacher, Sheba (Cate Blanchett), an artfully dishevelled thirtysomething blonde, full of noble intentions about inspiring her charges. To Barbara’s surprise, they become friends, and she’s invited home to meet Sheba’s husband (Bill Nighy) and their two kids. But when the older woman discovers a secret about her colleague, their relationship shifts a gear into something much darker and more sinister.

Much of the pleasure of Notes on a Scandal lies in watching Dench, shot from unflattering angles, play an increasingly crazed lesbian stalker, who’s consumed by misanthropic bile. Her acerbic voice, one of the key features of Zoë Heller’s original novel, is retained in screenwriter Patrick Marber’s and director Richard Eyre’s adaptation: an unfortunate fellow teacher is ‘a pig in knickers’; Sheba’s son with Down’s Syndrome is ‘a tiresome court jester’.

Blanchett proves an excellent foil in this black comedy, her bourgeois bohemian Sheba a woman of guileless charm, who still recognises ‘the distance between life as you dream it and life as it is.’ Accompanied by Philip Glass’ overblown score, Notes on a Scandal becomes less convincing in its melodramatic final stretches, but throughout it illustrates how timeless anxieties about class propel its characters’ actions.