ON Saturday of last weekend, I: watched Glasgow hairdresser Dotto Nalukala spend three hours braiding the hair of young model Luwam Khasay; followed young midwife Coco Bentgens’s demonstration of the ways in which babies exit the birth canal; saw an inflatable helter skelter explode into life as it filled with air while a troupe of young cheerleaders and dancers performed their high-energy routines; witnessed astrophysicist Nicolas Labrosse give a short, mind-blowing, illustrated lecture about the sun, and heard businessman Stephen Aloysius O’Neill announce, with absolute frankness, his annual income, which is more than 10 times the average wage in the UK.

I experienced all of this (and much more) in a 12-hour visit to the Tramway arts venue in ­Glasgow, and I did it in, surely, the only way it is possible to have such an extraordinary and diverse series of experiences in such a ­relatively short space of time: namely, by being a ­member of the audience for (and, in my case, also a ­participant in) the unique stage work that is 12 Last Songs by Manchester-based theatre ­company Quarantine.

The premise of this exceptional live artwork – which Quarantine defines as ­“part-performance, part-exhibition of people” – is to bring three ­professional stage ­performers together with around 30 people from a given city. The ­“workers” – who, in Glasgow, ranged from Tramway’s longstanding caretaker ­Sandra Stewart, to palliative care professional Lorna Reid and the aforementioned factoring ­company director, Mr O’Neill – are selected for the ­radically divergent jobs they do.

Each of the local participants does a shift in Tramway’s T1 performance space. Some – such as decorator Nicola McGhee, who turned a ­massive wooden surface into an excellent ­projection screen by covering it with lining ­paper – give public demonstrations of their ­particular skills.

All engage in conversation with the ­performers – Leentje Van de Cruys, Craig ­McCorquodale and Michael Sherin (who ­alternate in ­one-hour shifts) – who ask them questions about their ­professions, and posit questions from ­Quarantine’s list of 600 queries that range from the everyday (“what time did you wake up?”) to the personal (“how much do you earn?”), the political (“will you vote for ­independence?”) and the profound (“do you feel part of ­something bigger?”).

While this process takes place, sound and stage technicians are engaged constantly in the immense challenge of keeping the show ­running smoothly. Microphones must go to participants where and when they need them, and wireless mics must be turned on and off at the right moments.

Stage techs are in almost constant motion, making space safely for the movement (on and off) both of people and essential props, such as a dog grooming station or a miniature kitchen.

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Meanwhile, a fourth performer, Kate ­Daley, is out in the city beaming back live images from such varied locations as a rooftop bar in Finnieston, Central Station, and the country and western Mecca that is Glasgow’s Grand Ole Opry.

Occasionally, Daley pops back into ­Tramway to regale the audience with quirky and ­humorous stories of her encounters with the great Glaswegian public.

All-in-all, I was in the performance space – both as participant and in my professional role as critic – for more than 11 of the production’s 12 hours.

I can say with absolute honesty that – in a 30-year career that has had many ­notable ­highpoints, from interviewing such cultural greats as ­Harold Pinter, Liz ­Lochhead, ­Howard Barker, Fiona Shaw and Robert ­Lepage, to ­encountering brilliant and memorable ­productions from ­every continent – ­experiencing and participating in 12 Last Songs is among the greatest privileges of my professional life.

The reason for this is that the piece is ­conceived so beautifully, cleverly and ­generously that, over its dozen hours, it amounts – ­increasingly, subtlety and cumulatively – to a work of deep and moving humanism.

At times, the show’s attraction is its sheer ­variety – where else could you find yourself ­simultaneously watching an exhilarating and ­hilarious pro-wrestling bout between ­brother wrestlers Fraser Girvan and Lewis Girvan, ­painter Jim Ramsay creating a portrait of life model Faith Eliott, and chef Rukshan ­Weeraratne and his assistant Ellie Grey Scott cooking a delicious Sri Lankan vegetarian dish (which is then served as dinner to all and ­sundry)?

These living exhibitions – remarkable and quotidian – of the sheer breadth of human endeavour sit alongside the Quarantine performers’ uninhibited, direct, empathetic and witty questioning of the participants.

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Whilst the Manchester company provides the exquisite conceptual frame, the smart structure, and the brilliant performative and technical execution of the piece, it is the workers themselves who create the unique content.

In common, I’m sure, with every other ­production of 12 Last Songs, the outcome of the plethora of original spectacle and speech that was generated in Tramway was a veritable love letter to humanity.

It was impossible not to feel one’s faith in ­humanity nourished – just as our bodies were nourished by baker Ameena Nur’s ­delicious ­pastries – by the expression of lives that, while varying vastly, also speak to a common ­experience.

There is, undoubtedly, a universal dimension to the production – in which director Richard Gregory and assistant director Sarah Hunter lead an impressively talented and committed production team – as it moves from location to location.

However, because it selects participants from within its given city, it is also gloriously specific to its place.

In that sense, the Tramway performance was also very much a love letter to the city of ­Glasgow.

People like Kirsty Cleland (a housing worker with the Salvation Army) and Peter ­McDermott (a Glasgow City Council roads worker and ­volunteer with addiction charity Calton ­Athletic) express something particular, both about the nature of the social problems ­Glasgow has faced (and continues to face), and the ­manner in which working-class Glaswegians have addressed them.

At the end of the 12-hour marathon, a ­member of the Quarantine production team commented to me that the Glasgow show had been one of the more “gentle” incarnations of 12 Last Songs.

My home city proving, once again, that it has an almost ineffable ability to defy expectations.