In Sea Wall, Andrew Scott goes from being a great actor to being one of the greats

In the past six months, I have seen some astonishingly good theatrical monologues: Carey Mulligan in Dennis Kelly's Girls and Boys; Petra Letang in Random by Debbie Tucker Green; Anna Deavere Smith, still on stage nightly at the Royal Court, in Notes from the Field and Laura Linney, currently making the large space of The Bridge feel like a confessional in My Name is Lucy Barton.

What each of these do is use the form – one person, alone on a stage, weaving a story – to create a profound emotional impact. They use the skill of a single actor to conjure an entire world.

They work in different ways. My Name is Lucy Barton is adapted by Rona Munro from a novel of the same name by Elizabeth Strout and it still bears the imprint of its literary forbear. Some scenes and themes feel squeezed into the narrative where they expand happily on the page. Linney plays both a daughter and her mother, who arrives at her hospital bed and tells stories from their mutually unhappy past.

What's so impressive about Stephens' writing is the way that he uses half-phrases, sketchy reminiscence

In Girls and Boys, Mulligan is a mother, alone on stage, telling us the story of her marriage. But in scenes of eerie clarity, she steps into a monochrome living room and acts out scenes with her imaginary children. It is unsettling and bizarre and only gradually do we realise why it is significant. In random, too, Debbie Tucker Green asks a single actor to tell a tragic story, but here Letrang plays many parts: a teenage girl, her mother and father, the police, her bolshie brother. Those multiple acts of impersonation are taken to a different level by Deavere Smith who doesn't just suggest different characters but by changing her shoes and her delivery, actually embodies them, imitating the vowel sounds, the posture, the pose of the people she has interviewed and whose words she reports.

But even by these elevated standards, seeing Andrew Scott in Sea Wall, written for him in 2008 by Simon Stephens, is something else. It combines the reportorial, conversational qualities of such monologues with an understated poetry.

It is very short. As Stephens explains in his programme note, it grew from a specific commission – 30 minutes in natural light – and was written over three weeks. It takes bareness to the point of a white canvas by Rauschenberg. There seems to be nothing there, yet in the movement beneath the surface, in its metaphorical compression, it asks the biggest questions of all about the nature of life, the existence of God.

It begins with Scott on stage, watching the audience arrive, a small smile occasionally flitting across his face. Casually dressed, apparently entirely relaxed, pacing the space of the Old Vic, he begins to create an intimacy with the audience that deepens and engulfs us as he begins – still with the house lights up – to speak in the character of a photographer called Alex.

Monologues, because they rely on someone telling us something, can be over-stated. People can say things they wouldn't say because they know we need to know that thing. That doesn't happen here. What Scott says is full of half-sentences and swift changes of pace, just like casual speech. When he tells us about the sea wall, the precipitous drop into the unknown that he sees while diving, it seems like an off-hand anecdote, full of wonder and humour. But it is the central metaphor of a work which pivots on the terrifying depths that lie beneath the sun-dappled surface of everyday life.

"There's a hole running through the centre of my story, through the centre of me" says Alex. "You can see it, can't you?" And what is astounding about the performance, is that you can. Scott, for all his charm, for all his vivid descriptions, his gentle, insouciant recreations of the way his daughter throws up her arms for a hug, or the clipped tones of his ex-soldier father in law talking about mathematics, suggests an arrow of pain running through his heart. In front of our eyes, exposed on a blank stage, he creates a character, a man full of childlike innocence, a keen observer of life, who is destroyed by a single moment.

It is extraordinary, deeply moving and yet always restrained, an acting performance as much like a haiku as the play itself, finding all its effects in what is not said as well as what is spoken. There is one moment of pause so long and so intense that you cannot believe it will ever end. The theatre is utterly silent. We are all under the spell not just of the performance, but of the suffering we are imagining and sharing.

There is one moment of pause so long and so intense that you cannot believe it will ever end

I first began really to notice Scott and to seek out his work when I saw him (on TV) in the National Theatre's 50th anniversary gala, when he played a tiny scene from Angels in America. In an evening full of wonderful moments, this for me was the single most distinctive. It felt like an example of acting at its very best.

Of his Hamlet I can say little that I haven't already said, except that it seemed to me to reveal all the qualities that make Scott so fine: a sense of living in the moment, a quality of revelation, an ability to create a bond with an audience and take you inside his head.

All these qualities are here again in Sea Wall. It is a performance of blistering intelligence and wonderful emotional reach. Seeing Scott on the Old Vic stage held by so many great actors of the past, I felt I was watching one of the great actors of the present. He is something to behold and someone to treasure.