Old Vic, London Duncan Macmillan’s two-hander is a frenetic portrait of flawed love in a flawed world, exposing the neuroses of a modern couple who struggle to put their principles aside

‘The world is fucked,” says one half of the earnest couple in Lungs, fretting about starting a family on an over-populated planet. Since Duncan Macmillan’s play about modern love and the climate crisis was first staged in 2011, it feels like the world has become even more so. The script’s debates on individual responsibility for saving the planet take on renewed significance amid the rise of public protest and Extinction Rebellion.

The unnamed couple, played magnetically by Claire Foy and Matt Smith, worry about the polar bears and eating imported avocados. Their hand-wringing carries its own middle-class hypocrisies. They angst over the carbon footprint of a prospective baby (“10,000 tonnes of CO2”) and consider planting trees to offset the damage. But they sound like helicopter parents from the minute she gets pregnant. Their neuroses and double standards are gently derided, but the idealism to be “good people” is not undermined altogether.

Foy and Smith perform this two-hander after having honed their chemistry in Netflix series The Crown, and it is an achievement that they are not defined by those roles. These characters are instantly convincing as a trendy young couple arguing in an Ikea queue: she is a PhD student in dungarees and rolled up shirt sleeves, he is a new man in Nike trainers, nodding along to her stridency. Their rat-a-tat repartee of the early scenes is sharp and funny, but frenetic, too, and the drama gathers powers as it slows and introduces silences.

Rob Howell’s set design, like the original, is minimalist to the extreme, empty but for a solar-panelled floor and two tiles on opposite sides propped up by rock crystals – a sly satirical reminder of the couple’s fashionable, new age environmentalism. The bareness on stage forces the actors to do all the work; for Foy and Smith, it allows them to showcase their natural synergy, sometimes with a hint of swagger. But it also works on a metaphorical level in stripping their relationship down to its bones.

Facebook Twitter Pinterest Magnetic ... Matt Smith and Claire Foy. Photograph: Helen Maybanks

Their existential crisis is as much about sexual politics as it is about the environment. As an enlightened modern couple, they reverse traditional gender relations to some degree: Foy is more dominant, forcing her counterpart into the ancillary role as she monologues about the planet, motherhood and his predatory gaze when they have sex (“Sometimes it looks like you are going to hack off my limbs and bury me in the woods”). Yet she also demands old-style strength and initiative from him.

Smith, for his part, likes her honesty, but is paralysed by it: “I don’t know what you want. I need you to give me some clues.” In this bristling dynamic, they encapsulate the paradoxes of modern masculinity and empowered femininity, enacting its conflicts and contradictions brilliantly in scenes that range from comically bathetic to tender and enraged.

Matthew Warchus’s direction pits them against each other visually to mirror the verbal combat; they stand at opposite ends of the stage or circle each other in gladiatorial fashion when they are scripted to be lying in bed together.

Scenes cut away and change seamlessly so that day turns to night within seconds, a row turns into a sex scene, a breakup into a reunion. Foy and Smith manage the switches of mood and tone with a virtuosity that verges on ostentatious, and there are very few off-moments in pace. It is only the last sequence, in which times speeds up and characters, present and imagined, grow up, age or die within seconds, which feels rushed, gimmicky and riddled with cliche.

The couple’s principles are put to one side when life takes over. Yet the message of this play is not a cynical one. It is simple a picture of flawed love, set in a flawed planet.