I'll start with a digression, if a digression can be at the start. The other day, I bought some carrots. On the packaging it said Honest British Produce which aside from chiming uncomfortably with the anti-foreign, pro-Brexit mood of the country, which would deny even a home-grown aubergine a British identity because of its foreign lineage, still serves as a useful reminder that old fashioned simplicity can be a virtue.

I thought of those carrots during this adaptation of Khaled Hosseini’s award-winning book. The West End is awash with exotic, spectacular, celebrity-led shows, but this one — adapted by American writer Matthew Spangler and directed by Nottingham Playhouse’s Giles Croft — has a simple theatricality to it that is as bracing as the air over a freshly ploughed field.

The star here is the moderately famous by West End standards Casualty and WPC 56 actor Ben Turner. He plays Amir, the privileged son of a Kabul merchant in Afghanistan’s liberal 1970s. Amir’s best friend is Hassan, the son of a Hazara Shia family who has served Amir’s Sunni family for over 40 years. It’s a bond that climaxes in the winning of Kabul’s kite-flying tournament, a life-enriching tradition that would soon be banned under the Taliban’s barbaric rule but which the bookish Amir wins with the help of Hassan whose loyalty Amir later betrays.

For those who haven’t read the book or seen the film, Hoesseini’s story is at heart a confession of that betrayal, and an admission also of the guilt that Amir carries with him when he and his father move as refugees to San Francisco after the Russian invasion, leaving Hassan behind.

The contrast between Kabul and California is beautifully evoked, not by special effects but by the cast’s Afghan characters transforming into brash American archetypes. Meanwhile, the wooden fence that forms the background to the Afghanistan scenes becomes the city’s silhouetted skyline.

All simple but hugely effective stuff. And the moment has extra potency with the knowledge that were Trump’s anti-Muslim immigration ideas in place at the time that Amir or his creator moved to the USA, this and millions of other stories and lives that connect East with West would never have happened.

As Amir, Turner delivers a terrific performance evoking childhood and adulthood, but also Afghan and Western culture. But the show stealer is the small-framed Romanian-born actor Andrei Costin who, in his West End debut, plays Hassan.

It is a restrained and touching performance that one can’t help but wonder might have been denied this production if it had been created in a post-Brexit Britain with tighter immigration laws.

Elsewhere, the show is long and could do with a cut, preferably by getting rid of some of (presumably) Hosseini’s more whimsical prose. To give just one example, actually spring does not thaw snow “one flake at a time” but several million simultaneously.

Still, petty gripes and political pondering aside, this is theatre at its solid best. As nourishing as it is simple.