Economics on the stage? It sounds dry but this adds up to a night of frolicsome fun: PATRICK MARMION reviews The Standard Of Living

The Standard Of Living (Theatre Royal Haymarket, London) 

Rating:

They are peddling a very rare commodity at the Theatre Royal in London's West End: Optimism. 

The purveyor of this dangerous drug is none other than the moustachioed egghead and early 20th-century economist John Maynard Keynes.

Played with rueful gusto and comic frustration in a bashfully brilliant turn by Rory Kinnear, pictured, Keynes is the latest onstage subject for James Graham, the documentary playwright best known for his Gareth Southgate hagiography Dear England.

Right at the start, Kinnear's Keynes poses one of philosophy's oldest questions: What makes a good life? 

For Keynes it was the only question worth asking in economics. The market for him was an expression of human desires. 

'In the long run', he famously reminded us, 'we are all dead' – so we should get out and spend while we still can. 

'Money in savings is asleep, money spent is alive,' he once wrote. Try telling that to your chatbot bank manager.

What is most remarkable is that what might sound like a very dry subject is delivered by Kinnear as a fascinating, fun-filled and even frolicsome evening.

In a delightful performance, the actor humanises Keynes with a nervy air of uncertainty. 

A Cambridge-educated, anti-establishment establishment-insider, he was teased by jealously admiring friends in London's so-called Bloomsbury Group, a clique of free-thinking artists, including writers Virginia Woolf and Lytton Strachey (a snippy Naomi Frederick and neurotic Pip Carter).

Keynes's sternest critic, however, was a former admirer – the Austrian economist Friedrich Hayek (a neatly impertinent turn from Laurie Kynaston). 

He was a devout free-marketeer who witnessed the horror of hyper-inflation after the First World War.

Graham's portrait of Keynes is otherwise sunny and uncritical, admiring his chutzpah in standing up to the old boys' network and joking about his personal life (he kept a pocketbook record of one-night stands). 

But when the promiscuously homosexual Keynes falls for the flamboyant Russian dancer Lydia Lopokova (the Royal Opera's prima ballerina Natalia Osipova), he becomes more grounded.

In the absence of chaos in his personal life, Graham's story becomes blatantly didactic – even stooping to a direct plea for arts funding. 

Even so, director Nicholas Hytner ensures the story remains a lively pageant, swimming in projections of colourful artworks of the period as well as black-and-white news footage covering half a century of British history.

You don't have to agree with Keynes's free-wheeling economic theories – and he manifestly failed to save the world – but his story should keep you talking well into the night.