Whether Judi Dench, Helen Mirren or Kate Winslet, or none of them, wins this year's Oscar, Dench's performance in this exceptional film deserves to be accounted one of her best on screen.

Playing Barbara, a lonely and ageing spinster who teaches in a London school and suddenly finds she has the power to dominate Cate Blanchett's Sheba, a much younger member of staff, she is not just an ordinary villain. We see her vulnerability, her loneliness and her desperation to be loved.

"People," she says, "have always trusted me with their secrets. Who will I trust with mine?" It is this refusal to play some kind of latterday Lady Macbeth that makes this portrait so subtle and so powerful.

The married Sheba has trusted her with the secret of her affair with Andrew Simpson's attractive but emotionally needy pupil. And what Barbara wants, if she is not to inform the headmaster, is absolute power over her. This is the companion she has always sought, but in the end the liaison she seeks proves impossible.

Richard Eyre's film, skilfully adapted from Zoe Heller's novel by Patrick Marber, has a melodramatic ending which weakens it a little but remains, like Dench's performance, one of the best things he too has done for the screen. It is masterfully constructed, and contains several outstanding performances.

Blanchett as the wracked and guilt-stricken Sheba, Simpson as the lovelorn pupil and Bill Nighy as Sheba's patient, unknowing husband, whose sudden explosion when he finds out the truth is startlingly effective, add considerably to the strength of an adult movie with few Hollywood-like compromises.

If we can still make films like this and The Queen, the often beleaguered British film industry can clearly hold its head high in any company.