In the tunnel in Guadalajara, Sócrates stopped. One of the giants of Brazilian football turned around. He wanted to shake the hand of someone a few places back in the opposition line-up, someone who until that day Sócrates had never heard of.

That young man was already sweating. Fifa had decreed that the Brazil-Northern Ireland group game at the 1986 World Cup would take place in Mexico's midday sun. To the Irishmen in the tunnel, the light at the end signalled intolerable heat and humidity.

David Campbell had other reasons for perspiring. Ten days after his 21st birthday, some 20 games into his professional career with Nottingham Forest, and after just 24 minutes of international football, Campbell was making his full Northern Ireland debut. Against Brazil. At the World Cup.

And now Sócrates, 6ft 2in and counting, and nowhere near as tall as his status, was looming over the 5ft 9in winger from Derry.

"It was like a scene from Gladiator," Campbell says. "The Brazil team, with Socrates, were standing beside us in the tunnel. We had big Alan McDonald shouting something like 'we can do these, boys'. Sócrates stopped, walked back to me and shook my hand. He must have known it was my debut. It's a true thing."

Some 30 years on there is still awe in Campbell’s tone, and him adding “it’s a true thing” is understandable because there are elements of Campbell’s life that would make a film. Well, actually, they have done just that.

It is called Shooting for Socrates and was premiered in Belfast last night.

The story is David Campbell’s story and is set against the backdrop of the Troubles, not just ours but those of Brazil.

The 1986 World Cup was Brazil’s first after the dissolution of the country’s military dictatorship. It had lasted since 1964 and had in some cases erased opponents, in others eroded them. It is still striking to consider that the golden 1970 Brazil team caused some mixed feelings as Brazilians did not want others to think that by cheering the team they were cheering how their country was being controlled.

Pro-democracy rally

One who stood tall against dictatorship was the footballer/doctor, Socrates. In 1985 Sócrates addressed a pro-democracy rally in Sao Paulo. There were 1.5 million people there. Socrates’ club in Sao Paulo, Corinthians, had become “Corinthians Democracy” in 1982. They did not have names on the back of their shirts, they had “Democracia”.

Having not seen the film, I cannot vouch for it, but if it conveys the charisma and importance of Sócrates with the surprise and intrigue of Campbell’s career and life, then it has something. “Sócrates had this power over his country,” Campbell says, “while Northern Ireland of the ’80s was still in turmoil. But people tell me that for those 10 days or so of the tournament there was peace at home.”

That is correct. There was a murder roughly every five days in the North in 1986 but between June 3rd, when Northern Ireland drew 1-1 with Algeria in their opening game, and June 12th when they lost 3-0 to Sócrates’ Brazil, there were no killings.

It had been similar in 1982, when Northern Ireland had been in Spain for that World Cup. Then the murder rate was one every three days but almost a month passed without such news bulletins.

One personal effect of the Troubles was that the Campbell family relocated from Derry to Letterkenny. But David’s father James continued to work at the Coolkeeragh power station in Derry and David still went to St Columb’s College.

This meant early starts daily and David

would arrive at school long before other pupils. He used his time to kick a ball against a wall and became very good, so good that by 14 Brian Clough was aware of David and was stunned to discover his rivals at Manchester United and Liverpool were not.

"What had happened was that when I was 12½-13 I broke my leg," Campbell explains. "Getting fit, I joined Letterkenny Athletics Club. It turned out I was quite fast and had stamina, so I ran 100m and 800m. I got picked for Ireland and then was enrolled on the Mary Peters development programme. It looked as if my future was athletics.

Go over for a trial

"But I'd started playing football again and a man called Billy Melis recommended me to Forest. They wanted me to go over for a trial but St Columb's wouldn't let me go."

Eventually Campbell travelled to Nottingham. There he encountered the season’s final trial for boys invited from across these islands and Europe. Campbell stood out; Forest were confused. No other clubs were interested, yet Campbell was clearly a player. They arranged a second trial, watched by Clough, who then rang David’s father to see what the full story was. In that phone call Clough offered Campbell’s son a two-year apprenticeship, plus two years after that. Campbell was 14.

“Brian Clough was brilliant to me,” he says. “He called me ‘Irish’. He checked where I came from and said to me: ‘Well, Irish, Martin O’Neill’s from Derry and he’s done well for me. We’ve just won our second European Cup.”

Aged 15, in 1980 Campbell moved to Nottingham. "Forest had the likes of Peter Shilton and Trevor Francis, " he says. By 19 he was making his debut, and at the start of 1986 the surname Campbell began to appear regularly in Forest's starting XI.

There had been homesickness, now there were goals – at Highbury and Maine Road. Clough wondered aloud if Billy Bingham would pick Campbell for Northern Ireland and in the last warm-up before heading across the Atlantic, Bingham did. Campbell got 24 minutes against Morocco, replacing Norman Whiteside.

One place vacant

Martin O’Neill’s injury meant there was one place vacant in Bingham’s squad and it went to Campbell, which is why, after such little experience, Campbell was on the same pitch as Socrates. And when Sócrates went off, Zico went on.

The game was historic. Pat Jennings, on his 41st birthday, was playing his 119th and last international. Jennings sat beside Campbell on the bus to the ground and in the changing room. After the match, made famous by Josimar's thunderbolt goal – Campbell got Josimar's jersey – he witnessed the Irish squad cry at the end of an era.

Campbell thought his had only just begun, but as he says: “Within 18 months I was lying in a Bolton hospital with a leg broken so bad the doctor thought they might amputate.”

He made several comebacks, and played a season with Shamrock Rovers. Campbell says he has Noel King to thank for making him plan his post-playing career.

Campbell set up soccer schools and is still running them successfully 20 years on. Those boys and girls have some story to hear.