Since the rise of James Graham and his fascinating parliamentary play This House, David Hare is no longer the undisputed champion of political playwriting in this country. But director Stephen Daldry's beautifully judged revival of Hare's 1995 post-Thatcher play is a reminder of the finesse with which this heavyweight integrates political argument.

Bill Nighy is restaurant entrepreneur Tom and, in her West End debut, a captivating Carey Mulligan is idealistic school teacher Kyra with whom Tom had an affair. Bob Crowley's terrific design centres on a high-rise block that overlooks the grubby interior of Kyra's Kensal Rise flat, where all the action takes place. The block's windows are brilliantly used to suggest the passage of time as lights go on and off and the sound of children fades in and out.

When the now-widowed Tom visits to reignite the relationship, the former lovers' talk is not just of nostalgic memories about the days when Kyra worked in the family business, nor about her status as close family friend. It's about the values that drive her to become a teacher of children in a deprived area and drive him to build an empire of posh restaurants in west London.

The evening is not only defined by two arguments, but by two very different acting styles. Mulligan is a joy to watch. There is a sorrowful stillness to her Kyra that suggests the deep wound sustained when she abruptly left Tom after his wife found out about the affair. Nighy's Tom is the complete opposite. His voice is perfect, that of a by-the-boot-straps businessman who has made good. But physically it's a puzzling performance. He darts around the stage, gesticulating with every syllable, kicking chairs and making sudden diversions that have no destination. Sometimes he stands with his back to the audience in a quasi rock-star pose.

I can see the need for contrast - it's the clash of personality that makes them interesting. But Nighy's posing needs reining in to prevent it from being distracting. Iron out some of that and you have a play that gets to the heart of the debate about addressing inequality in Britain, and also to the bruised hearts of two probably doomed lovers.