Shaftesbury Avenue: a street that blinds you with bright lights, mighty signs and five stars. You get bedazzled by the offerings and bashed by tourists happily taking 20 minutes to walk two metres. Not the best environment to be hunting for a black door in an alcove between Les Miserables and The Curious Incident of the Dog in the Night Time. An usher in a butcher’s apron huddles me in through the suitably ominous entrance. I make my way down darkened corridors fully expecting the demon barber of Fleet Street himself to jump out at me at any point, finally reaching a nerve-calming bar, with themed cocktails to add to what is already taking a musical way beyond theatre and into a full-blown experience. Armed with a blood-coloured yet surprisingly elegant cocktail, I wandered around the black basement bar, noticing detail after detail: a Victorian till, photographs of close shaves through the ages, Sweeney Todd’s fictional letter, all piecing together a mood before the house even opens.

Inside is an impeccable replica of Harrington’s Pie and Mash Shop, Tooting’s finest, where this production was first shown. A putrid colour scheme, hanging menu and long vinyl-coated tables that we are told in no uncertain terms to keep empty of drinks and elbows. We soon learn why as the unified force of an ensemble take interactivity to a whole new and more menacing level. Clambering, towering and sitting amongst us as the twists get tighter. The seating is snug to say the least but that only intensifies the atmosphere. The room only gets smaller as the mood and the lighting get darker.

Jeremy Secomb’s Sweeney is gaunt and hauntingly undistracted in his cravings for blood. He is both transfixed and vacant yet there is a strange kind of heart to his characterisation. His voice is mesmerically powerful. His Mrs Lovett, played by Siobhan McCarthy, is warm and attractive. She strikes a perfect balance between tactility and torment. The friction between them hurls so much momentum into the plot that it’s hard not to get carried away with it, dragged into the snowball of their action. The close proximity of the entire ensemble is beguilingly captivating and startlingly eerie. The brilliant pianist was on my immediate right and his insistent chiming made my heart beat that bit faster.

This version of Sweeney Todd is utterly inescapable, you are so involved in it that you can’t help but think you could be next in line for the chop. It is stuffed full of character, detail and undeniable talent, then wrapped in crimped pastry of tantalising charm.

Sweeney Todd is playing at Harrington’s Pie and Mash Shop, Shaftesbury Avenue until 30 May. For tickets and more information, see the Delfont Mackintosh website.