Sarah Sands: Emma Thompson is the true lady of Brideshead

"It's our turn now," says the young soldier at the end of Brideshead Revisited, and so it is. Do not mind the old incumbents who moan that Diana Quick can never be robbed of her role as Julia Flyte, or that Jeremy Irons conveyed more emotion as Charles Ryder. Instead, there is a fashionable distaste for barmy old faith and self-restraint. Brideshead has become better looking and more shallow.

That is, until the entrance of Emma Thompson as Lady Marchmain, as resounding as the first chords of an organ. Lady Marchmain may crucify her children with her faith, but her dignity and will are at the centre of the novel and the film. She arrives late in the action and dies early, but Thompson makes her the most memorable character in the film, never warm, but passionate and compelling.

Unlike the rest, she sees Charles Ryder for what he is – a bloodless and selfish social climber. Like all great screen actors, Thompson conveys great feeling with little movement. It is all in her wonderful face. When she accuses Ryder (Matthew Goode) of betraying her son by giving him money for drink, it is not her words that shock, but the hardening of her expression. If this film is a secular polemic against the evils of faith, Emma Thompson's acting throws the screenplay into disarray. She and Michael Gambon put the young pretenders in their place. This is no time for novices.

We have grown used to the old dames – Judi Dench, Helen Mirren, Maggie Smith; there is no one much else until you reach Keira Knightley. Thompson is surely the successor to Dame Judi, the best actress of our times on suffering borne with poignant dignity. I first started to love her in Sense and Sensibility, where she made Elinor Dashwood, the practical, dull sister, heartbreakingly intricate. I loved her most of all in Love Actually, where she stole the emotional narrative from the romantic protagonists with her portrait of the betrayed wife, pulling herself together in the privacy of her bedroom. And I love her again in Brideshead for the great depth and intelligence of her acting.

My companion at the cinema, who carries a torch for Diana Quick and still considers Caroline of Monaco to be young and racy, was a touch disgruntled by Thompson and further put out by Greta Scacchi. Couldn't they make a bit more effort, in the manner of Demi Moore or Sharon Stone? Actresses over 40 traditionally chase youth with demented zeal or become invisible until they are old and ugly enough to play character parts.

Emma Thompson has done something extraordinary for her profession and for all women. She is ageing in real time, growing in stature as she become etched with lines. As she starts to resemble her mother, Phyllida Law, she shows the same strength of character. But it is not a self-congratulatory, inward-looking, "I Will Survive", TV-feminism strength. Emma Thompson is laughing through tears, touched by the seriousness of life, remarkably empathetic, astonishingly generous. Her friends say that the feeling in her acting exists in real life. She is Elinor Dashwood. Many of us become shrivelled by life, but Emma Thompson has grown. She is the same idealistic, intelligent woman that she was at Cambridge, but life has made her more humorous and compassionate. Experience has given her character and judgement. It has made her one of the great actresses of our generation and a rare role model.

Sarah Sands is editor in chief of British 'Reader's Digest'