The chances are you won't have heard too much about the Scottish Unity League or its pithily named teams such as Oasis, Universal or Fusion. Their match reports don't appear in the newspapers, nor do the scores. They don't get an hour and a half on Sportscene, or a place on the Sky Sports vidiprinter, either. You may have heard of some of the league's former players, though.

The Peterborough United midfielder Siriki Dembele once played for Calabash FC. Celtic fans might know his brother, Karamoko, who has also featured for the team. Another former Celtic child prodigy, Islam Feruz, cut his teeth on the parks of Glasgow Green, Scotstoun, Firhill and Toryglen, so too did Brian Graham, the Partick Thistle striker, formerly of Morton, Dundee United, Ross County, Hibernian, who made his debut in the league at the age of 15. Another boy, known simply as Abdi, is now training with Chelsea's Under-19s.

Despite its unaffiliated status, Abdul Bostani, the league chairman and founder of one its most successful teams Glasgow Afghan United, says the standard is incredibly high as some unwitting opponents found out to their cost one day in a pre-season friendly.

“One of the teams [from another league] asked me to come to play a warm-up match,” says Bostani. "They said: 'we'll pay for the park, we'll pay for the pitch'. They were saying 'please bring good players, don't waste our time'. The manager repeated this a few times, so we agreed. He booked a park at Glasgow Green, they had a lot of people around volunteering for them, they had a camera and stuff like that. It looked like a very good set-up. I said 'we will do our best, my friend'. So we played the first half and we were leading 7-2 at half time, and then when we put on some really good players we couldn't stop scoring. We were laughing because the guy had phoned me three or four times to tell me to bring good players.”

As the name suggests the Scottish Unity League exists to provide an opportunity for all – so long as participants sign up to a constitution that places inclusion, good character and respect at its heart. Formed by friends Peter McLean – a well-kent PR figure on the Scottish football scene – and Paul Morrison in 2000 to give asylum seekers and refugees the chance to play regular football, it has gone from strength to strength in the 20 years since. Bostani, who fled Taliban-gripped Afghanistan in 2001 at the age of 18, says the pair more than achieved their aims. Today the league boasts a wide-and-varied representation, beyond that early remit, featuring in teams every Sunday.

Of his Aghan United team, he says: “We have Scottish, French, Ukrainians, Zambians, Tanzanians, Cameroonians, Afghans, Kazakhs and Iranians. There are players from America and New Zealand. We hold a tournament every year at the Refugee Festival of Scotland on World Refugee Day. We had 24 teams last year, there is always a great demand, and there were over 50 nationalities who played in it.”

The league is not affiliated to the Scottish Football Association, where running a team can cost up to £2000 per year, for reasons of financial pragmatism but also of principle. Unlike other leagues, the Unity League has a zero-tolerance approach to racism with automatic three-month suspensions handed out to transgressors pending a full investigation. While there have been instances in the past, Bostani has not had a case to deal with in his four years as chairman.

“Over 200 people every week come together, and for example, if one slot is at 12 o'clock the team will watch the games at two o'clock and they in turn will watch the game at four o'clock. There's a real sense of connection. All players know the other teams' players and where they are from, and at the end of those games they go into the town together, they go to the pub or the cinema. We have a lot of Scottish boys coming together and these people are making friends. They spend a lot of time laughing. It is like a family for them.”

The greatest challenge comes in the form of money. It costs £96 to book a pitch for two hours and £40 for the hire of a referee. Often it is the manager of the teams who has to pick up the £20-£30 shortfall just so that penniless players can get a game.

“They [the players] are walking five or six miles to play games because they don't have a bus fare, they don't have any financial assistance. I've seen boys walking from Scotstoun to Maryhill Road. In most cases, these boys aren't saying 'I'm skint, I don't have money' because they are shy and they don't want people to laugh at them. They still have their pride but I know that they cry from inside. I now go and pick up boys in my car. They love to come and play but they don't have that £5 to play. They are unemployed. As soon as I notice, I will say 'okay, our team will sponsor you'.”

Despite those financial hardships, the league is an overwhelming success and its cup competitions carry the names of those who have stood against injustice. The Glenn Gibbons Cup is named after the former Scotsman sports journalist who opposed and challenged sectarianism in football and in Scottish life.

The other knockout competition is played in summer and carries the name of Rio side Vasco da Gama, the first club to play black players in middle-class 1930s Brazil. Each year, when the cup is handed over to the winning team the story of how Vasco da Gama changed the course of history is read out and the man of the match is presented with a Vasco da Gama shirt.

The Unity League story feels particularly relevant at a time when the world is watching events in America with open-mouthed outrage. Jermain Defoe, the Rangers striker, said yesterday that racism exists everywhere following his experiences at the hands of police in England but Bostani, whose Afghan United programme, born out of a five-a-side team he formed with fellow refugees, is more circumspect. He agrees there will always be isolated instances but that Scotland has provided him with opportunities he could never have dreamed of when he left Kunduz Province on the Tajikistan border almost 20 years ago.

“In Scotland we have a leader who is very supportive of ethnic minorities. The government sees us as an asset of the country. If you are an ethnic minority you look at what the head of state of that country's attitude is towards you. Donald Trump is the most stupid president there has ever been. He should look at Scotland, he could learn a thing from Nicola Sturgeon and how the Scottish government has sought to include ethnic minorities.”

“I was a child when I came here in 2001. I was just 18 and I had no hope, actually. In Scotland, I was allowed to educate myself. People were pushing me to go and study. I had the same opportunity as my neighbour next door, I had the same rights of education. And I educated myself. My first degree was in accountancy from the University of Strathclyde and last December I graduated from Glasgow University having done a masters in community development and I had the same opportunity as anybody else in my class.”

Today, through the help of the Scottish government and others, Afghan United offers volunteer support and medical supplies to people who are isolated, it offers charity work and local services, a women's empowerment programme, a full education progamme, and a school with seven classrooms where more than 100 children receive cultural and homework support.

“I am a citizen of this country,” he says of what he has tried to give to it. “My citizenship comes first – I am Scottish, my heritage comes after that, I am Afghan. We are all living together.”

It seems it is not just the young who can learn from the good work of Bostani; there are lessons for all of us in his efforts – and those of the Unity League and its founders.