1999: Drumchapel High School, then considered one of the toughest schools in Glasgow, receives its share of children from asylum-seeking families who had been moved out of London. They don’t speak English, they’ve never been to Scotland; have they, as local girl Emma (Kara Swinney) asks, been sent north because Glasgow’s such a friendly place? – or could it be ‘because it’s got a lot of flats nobody wants?’

‘You sing when the character’s emotions become too strong for the spoken word’

Noreen (Terry Neason), matriarch of the Scotstoun flats and newly-minted activist, speaks this line with cynicism (she never wanted to be in a musical in the first place), but in Glasgow Girls, Cora Bissett’s visceral play about seven teenagers taking on the immigration service, only song is powerful enough to convey the passion of a story that has even greater resonance today than when it was first staged in 2012.

Despite the odds, Roza (Sophia Lewis), Ewelina (Stephanie McGregor), Amal (Aryana Ramhkhalawon) and Agnesa (Chiara Sparkes) soon settle in, and for a few years all goes relatively well. They are blessed with an excellent teacher, Mr Girvan (an outstanding Callum Cuthbertson) who, despite trying to teach them English via the lyrics of the Proclaimers and the Corries, swiftly becomes their ally (‘I do often think of English as a foreign language myself’). Cuthbertson’s recital of Burns’ To a Mouse is both hilarious and poignant; the mouse has seen his home destroyed too.

In 2005, the situation changes. Many asylum claimants still haven’t been granted settled status when letters start to arrive, the infamous dawn raids begin, and families disappear. When Agnesa doesn’t turn up for school, the girls discover her family has been taken in handcuffs to Yarlswood detention centre; soon they will be repatriated to Kosovo. The government says Kosovo is now a safe country – but Agnesa is Roma, and for Roma families there is no safety in Kosovo. Naming themselves ‘The Glasgow Girls’ Agnesa’s friends, backed by Mr Girvan, decide to take action.

What happens next is told in a series of horrifying tableaux. The thundering of truncheons on doors, the tearing of children from their beds, the loudhailer voices of the Border Agency staff, all bring home the violence and terror inflicted in the name of law enforcement. In one particularly shocking scene, a mother is surrounded by agents who block her every move as she attempts to escape. Soon she is on the floor; soon afterwards she and her five year-old son are on a plane back to the Democratic Republic of Congo. The dance numbers performed by the Border Agents are especially well choreographed, their movements robotic, their voices monotone. They’re ‘just doing their job’.

As the Glasgow Girls’ efforts to free Agnesa ramp up, their campaign starts to attract the media; soon they are on the radio, in the papers, and finally at Holyrood, where they’ve persuaded Jack McConnell to press their case.  The then First Minister – the immensely versatile Callum Roberston again, in one of his several guises – swithers; can he support a cause that won’t win him any votes? Robertson’s rock star-style portrait of a man with good intentions who’s become too much a part of the system to carry them through is painfully accurate.

One of the many strengths of this play is that it doesn’t fall into the trap of depicting the Border Agency as the sole enemy. In a radio phone in, one caller after another disagrees with the girls’ campaign – ‘I’m all for being nice to people but…’, ‘these people aren’t in danger, they’re playing the system’. There are divisions at home too – Emma’s Dad refuses to sign their petition, Amal’s mother urges her not to rock the boat. And while Agnesa’s family is eventually reprieved, Glasgow Girls is not simplistic – another family is not so lucky.

There are no weak performances in this production, but Terry Neason’s Noreen is a triumph – a Scotstoun woman who’s old and tired enough to know that the girls may never win against the system, but still cares enough to help them try; a mother who watches the children in the park way below her high rise kitchen, who can ‘see the dark clouds coming’ but still gets up at 5am to warn families to bolt down the fire escape when a dawn raid is imminent. Neason’s diction is exceptionally good, even when she’s speaking broad Drumchapel Glaswegian we can still hear every word, whereas my one quibble with this otherwise superb cast is that some were hard to hear at times. Neason’s singing of It’s No a Wean’s Choice is heartbreaking.

At a time when more and more borders are closing, Glasgow Girls celebrates the courage of some ordinary people who chose to reach out and fight for their fellow human beings, some people who did not give up. As Noreen says, ‘We invented solidarity in the Clydeside tenements.’

Glasgow Girls is at the King’s Theatre, Leven Street, Edinburgh until Saturday 26 January more information here. The play then continues its tour to Perth, Inverness and Dublin.