Willy Russell says the plot of Blood Brothers came to him as he was walking along: “I lifted my right foot and by the time I put my foot down I had the story.” One small step for a man, then, but a mighty big step for Mr Russell — and his bank balance. A fixture in the West End for 20 years, a hit on Broadway starring the likes of Petula Clark, David Cassidy and Carole King, a popular touring production at home and abroad — the show has coined it magnificently for a creative talent with the versatility to supply book, lyrics and music.

Its appeal is not hard to understand, with a heartbreaking tale on almost mythical scale matched to music whose plangent beauty and portentous power serve to underline the sombreness of its theme.

We meet a working-class mother, Mrs Johnstone — superbly portrayed by the 2007 X Factor semi-finalist Niki Evans — who is persuaded to give away one of her newborn twins to her childless employer (Tracy Spencer). Eddie (Paul Davies) goes on to enjoy every comfort that a well-moneyed home can offer, while Mickey (Sean Jones, pictured with Niki Evans) grows up as one of a houseful of kids on which Mrs J, having been abandoned by her feckless husband, is able to lavish love but not money. Toff and tatterdemalion eventually meet, as they inevitably must in a drama driven by an inescapable destiny repeatedly underlined by the omnipresent Narrator (Robbie Scotcher). There follow hugely enjoyable culture clashes as the two become firm friends, indeed the cowboys-and-indians-style ‘blood brothers’ of the title. The hilarity of their early scenes together are heightened by the fact that these two very different seven-years-olds are played — and played brilliantly — by grown-up actors. There is wonderful work, too, from Kelly-Anne Gower as their feisty pal Linda.

We need all the humour the show can supply, though, in view of the dark turn to come. Mickey is drawn into crime by his badhat older brother Sammy (Daniel Taylor), and a fall-out over Linda, now Mickey’s wife, propels the story to its tragic climax.

Until Saturday. Box office: 0844 871 7652 (www.ambassadortickets.com/miltonkeynes).