Ah, the menacing beat: attend the tale of Sweeney Todd! Who served a dark and vengeful god! It’s the familiar Sondheim masterwork, but never so thrilling, dark, wild and truthful as under Jonathan Kent’s direction. Under a high gantry where the orchestra beats out demonic energy, the labouring poor struggle, eat or are eaten: the costumes suggest 1930s rather than Victoriana but injustice, poverty and revenge are timeless, as is tragedy.

And it is a tragedy. You can play it as mere black comedy, and this is not neglected: Imelda Staunton as Mrs Lovett is fabulously funny from her first dishevelled extolling of The Worst Pies in London, and storms of merriment from the house accompany the patter song where she and Sweeney work out which professions make best eating. She is touching, too, in her lonely dreams of love, and miraculously keeps us on her side all through the cannibalistic pie boom, only sinister in the last horrid moments.

But if Staunton’s evolution is satisfying, Michael Ball is a revelation. We all know he is a safe pair of lungs, but his Sweeney is intense, pitiable, real. The journey from victim to avenger to serial killer takes on a kind of grandeur. This suits Sondheim’s score and lyrics, which veer from playful melodrama to fiery staccato energy and to romance.

The abduction and rape of Todd’s wife is brutally re-enacted high above; the Judge’s intention to marry the stolen child made properly repulsive. Ball’s dream that razors shall “float across the throat . . . drink rubies!” becomes comprehensible. When he fails to kill Turpin and turns with curdled flippancy to random murders, we believe the transition. In the melodic song of fatherly yearning, Ball’s Todd slits throat after throat with truly operatic flourishes, tipping the bodies down a steep (I hope, well padded) chute to the bakehouse. But when at last he cradles the dead beggar-woman, you think of Lear or Oedipus. Honest. It’s that good.

It all is: not least James McConville (fresh from Lord of the Flies) as Tobias: he deploys a reedily strong Sondheim voice in this difficult score, handling youthful energy and horrified pathos with assurance. Anthony Ward’s initially restrained set slides into nightmare: the oven, at first just hinted at with glow and smoke, rolls closer like the fires of hell. So does the big mincing machine: not onstage for long, but long enough.