The Line of Duty star helps people with dementia put on a concert, showing the magic of music even when everything else starts to fall away

“A mind like a sieve” is the saying for someone forgetful. In Our Dementia Choir With Vicky McClure (the Line of Duty actor, whose grandmother had the condition), a brain scan of a person with Alzheimer’s showed the truth behind the cliche. Dark gaps appeared amid what should be bright white solid places holding healthy cells and tissues, skills and memories, now full of spaces scattered by a limitlessly cruel hand of fate.

Music, though, often remains after other things have gone. Lyrics learned long ago can be embedded too deep for the ravages of age to erase them. The power of notes and harmonies to uplift, move and connect synapses and people remains potent. With this in mind McClure and a team of musicians and neurological experts (and the BBC in conjunction with the Open University) have brought together a 20-strong group of people with different types of dementia, from McClure’s home town of Nottingham, to form a choir that will give a public performance in a 2,000-seater venue in three months’ time.

Betty, 82, was diagnosed with Alzheimer’s three years ago. She is increasingly confused and absent-minded, but sings like an alto angel. Kellie, her granddaughter, helps to look after her. “I’ll miss Momma,” she says. A pause. “I already miss Momma. But … it’s about accepting a new Momma.”

Chris, 67, has fronto-temporal dementia, which attacks the areas of the brain that control behaviour, personality and language; the bits that make us most “us”, if you like. He is becoming more outspoken and inappropriately behaved. Perhaps as part of it, he seems sunnily unconcerned by the condition. His wife, Jane, who has taken early retirement to care for him, says: “It’s like the long goodbye – every week, every month, we lose something of Chris. He’s not the person I married. I just find the whole thing so, so sad.”

Julie, 50, and Mick, 51, have early-onset dementia, but youngest of all is 31-year-old Daniel. He has a rare form of genetic dementia that – he and his wife discovered after his diagnosis a year ago – killed his father at 36. Daniel’s expected lifespan is a little less than that. He is keen to take part in the medical study accompanying the choir project in the hope of enabling advances that will, in the future, help their two-year-old twins, who have a 50-50 chance of developing the condition.

The choir starts learning Stand By Me (as arranged by their choirmaster, Mark De-Lisser, for Harry and Meghan’s wedding). Betty, Chris and Mick are soloists unafraid to belt out a tune, and Julie builds up her confidence with every outing. McClure is genuinely involved in rehearsals, as well as fulfilling her role as presenter and interviewer, gently soliciting people’s stories and offering sympathy and empathy without sentimentality or strain. The programme takes the same approach. The choir members and those who look after them speak for themselves, and there are no contortions to fit anyone on to a particular path and force “a journey” on them. Everyone’s dignity remains intact and the blind cruelty of the condition is left to tell its own story, even if the harsher realities of their lives are not dwelled on.

What fills the gaps where lesser documentaries would have resorted to narrative trickery is the love of the carers for their relatives. Kellie’s approach is emblematic of it all – a love that expands, reshapes and envelops new situations and, ultimately, new versions of people, because humanity is extraordinary.

And the choir members look after each other. Julie has never sung in public before and after weeks of rehearsal remains nervous. “I’ll mother you,” says Betty, putting an arm around her. “You do put yourself down! We’re great friends,” she explains to the camera. “And we’ve only met today!” “No,” says Julie. “We’ve met a few times before, here.” Put two sieves together, you see, they catch more.

De-Lisser encourages them to have one person in mind when they sing Stand By Me (whose first outing will be at Daniel and Jordan’s pre-wedding party). Mick says it will be his wife, Karen – “But don’t ever, ever tell her!” Chris insists that he should. “I think she would enjoy hearing that from you.” Sometimes a lack of inhibition can be an advantage.

They sing about skies tumbling and mountains crumbling, and tears flow unstoppably among the people listening; their darlings, who will catch them as they stumble and fall.