On a dark, wintry evening in the Rhondda Valley, southern Wales, the hills that surround the village of Treorchy are barely visible against the sky. A road stretches upwards towards the ridge, where the Christmas tree lights sparkling in the windows of the small terraced houses are reflected in the puddles on the pavement. In the distance, the bright windows of the primary school stand out against the gloom.

In the school hall, a handful of men are standing around chatting – about recent rugby matches, mutual friends’ kids and the tricky matter of deleting an unwanted Facebook account. They are middle-aged and warmly dressed in jackets, jeans and jumpers. More men like them are arriving every few minutes, with some of the older ones entering the hall with sticks or supported by younger mates.

They are members of the Treorchy Male Choir, and they are here to sing. Once everyone has arrived (tonight, about 60 are present), they line up facing the conductor and begin. The sound is rich and full, with four-part harmony stretching upwards from the bottom basses to the high tenors. Their accents are clearly audible in the rolled Rs and lilting cadences of the music. It’s a sound that is synonymous with Welsh culture and life – heard everywhere from the area’s chapels to its rugby fields. Yet in the valleys, being in a choir such as this is an increasingly unpopular occupation.

As a result, the average age of choir members is rising. The majority of them are over 60 and many are retired, explains the secretary, Selwyn Jones. “A lot of the audiences are the same age as us and are dying off as well,” he says. They have a busy programme of events lined up over Christmas, though – they sing in old people’s homes, in children’s hospices and for shoppers in the village.

All-male choirs are part of a centuries-old musical tradition in Wales. They emerged in the 19th century out of the singing in Nonconformist chapels and the groups that, because of the Industrial Revolution, came together to work in the country’s mines, shipyards, factories and docks. The Treorchy Male Choir was formed in 1883 and was soon winning national musical competitions, known as eisteddfods. It performed at Windsor for Queen Victoria in 1895 but disbanded in 1943 while Wales was suffering from the effects of the Great Depression and two world wars.

The present choir was reformed in October 1946. Its two oldest members, Norman Martin and Islwyn Morgan – now 93 and 89 – joined in their twenties when they left the armed forces at the end of the Second World War. “Music had always been in the valleys, so when the choir started again after the war, that was the only place to go,” says Martin. For Morgan, music was a family tradition. “My father was a choir conductor, so the family were always interested in singing,” he says. “I’m one of ten children, all in different choirs. At one time, we were four brothers in this choir.”

After numerous competition wins, the Treorchy Male Choir landed a record deal with EMI in the 1960s and was invited to perform all over the world. “We wouldn’t have got out of the valley without the choir,” says Martin. He remembers the first time he went on an aeroplane, when the choir was travelling to perform in Switzerland, as a particular highlight. “This choir’s opened the world to us. Not just the valleys, or Wales, or England, but the world.”

Martin, a former miner, and Morgan, a retired council worker, no longer take part in concerts or tours. “Sometimes we don’t get back from a concert until three or four in the morning, and I’m finding that a little bit much at my age. But that’s the only complaint I’ve got,” says Morgan.

But both men still come to the two weekly rehearsals. “The comradeship, that’s what I like about it. Most of my friends are connected with the choir,” says Morgan. He recalls fondly the days when the choir had a third weekly rehearsal, too, on Sunday afternoons, for which often more than 100 members would turn out to sing together after attending chapel in the morning. “Of course, people aren’t so religious now.”

The fortunes of the choir and its ageing membership in the past two decades reflect those of this area of Wales. “There are no jobs,” says Selwyn Jones. “These areas were industrial areas or mining areas, and when the heavy industry goes, very little light industry has come in to replace it, so people have to travel to work. Then if they go off to university, they have a better chance of getting jobs away than back here.”

South-east Wales has the highest rate of unemployment in the country, and studies by the Joseph Rowntree Foundation show that almost a quarter of the Welsh population lives in poverty.

Jones says that recent research has shown that there has been a 20 per cent drop in choir membership in the valleys in the past ten years. “The challenge is getting younger people involved, but young people today have got so many other interests. Back in the day, you had the chapel or the church, the pub, the club and there weren’t any sports centres… Life has changed completely.” Further west, he says, where the Welsh language and traditional culture is stronger, choirs are doing well – but here, where the area is more anglicised, it is harder to attract new members. About half of the choir’s members still live in the valleys, with others travelling in from further afield. Most still have relatives here or ties to the area – the choir and its music act as a kind of diaspora link.

From the beginning, the choir has relied on the close friendships between its members. “They worked together, they played together, they socialised together, they drank together and they sang together,” Jones says. Looking around the rehearsal room, where the men are joking around, sharing music and making plans for beers over Christmas, I found it easy to identify that close comradeship still.

They might not get to work down the mines together any more, but this choir’s members will keep singing together for as long as they can.