Don King is singing the praises of his new signing. The boxing impresario, played by Zach Levene with an extravagant bouffant, sees something special in John Conteh, the light-heavyweight champion. It is a talent that goes beyond the ring. “He walks into a room and the air changes,” he says.

Impressively, this is a quality captured by Aron Julius. Playing the Kirkby kid who became WBC light-heavyweight champion in 1974, he is muscular, light-footed and graceful. More than that, he sparkles. With a needling Liverpool wit, he is as cheeky as he is charming. Who wouldn’t want him to win?

The best sequences in this bio-drama, written by Julius himself, are when Conteh is alone on stage giving a punch-by-punch account of his bouts, from the outsider success against Chris Finnegan at Wembley to the narrow 1980 defeat against Matthew Saad Muhammad in Atlantic City.

Only one man knows what those fights felt like and Julius captures a sense of the solitary sportsman holding his focus in the midst of public acclaim. He writes those scenes in crisp poetry and performs them, under the eye of fight director Rebecca Wilson, with vivid, bruising detail.

Dramatically, it is constrained by the facts of the rise-and-fall story, but as sporting bio-dramas go, Conteh punches higher than most thanks to the tensions in the boxer’s private life. His oft-repeated belief that “fights are won and lost on the training ground” is put to the test as his brother Tony (Levene again) tempts him to boozy three-day benders and Don King seduces him with a life of celebrity.

His manager George Francis (an agile Mark Moraghan) barks him back into line, bolstered by George’s wife Joan (a no-nonsense Helen Carter). In what could have been a male-dominated drama, Conteh’s wife Veronica (a defiant Amber Blease) makes feminist protests about being treated as an afterthought.

It is pacily staged by Mark Womack on a set by Zoe Murdoch in which the ropes of a boxing ring double as barriers and fences, while sound designer Kate Harvey slips in a soundtrack of cool 70s funk. The play fizzles out into therapy-speak as the boxer confronts his alcoholism, but with the ever-dapper Conteh himself joining the first-night curtain call, it goes the distance.