No sooner has the engaging Kenny Shiels fixed our coffees than he is off, totally flying.

No wonder this Northern Irishman is viewed as one of the most refreshing things to happen to Scottish football. For a man raised on a South Derry chicken farm, Shiels possesses a fine polemic that goes way beyond poultry.

He confesses he is earning relative peanuts as manager of Kilmarnock and hopes to claim at least one fat pay-cheque before he retires. But my mere mention to Shiels that he might one day fancy being an international coach triggers his evisceration of the current international scene, ruined in part, he claims, by innocent pawns such as Phil Bardsley, Aiden McGeady and James McCarthy.

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"International football has lost its identity since they brought in the grandparent rule," Shiels says. "It is absolutely ridiculous. How can Scotland bring up guys like Phil Bardsley, who is English, or Kris Commons, who is English? These are not Scottish people – they should not be playing for Scotland in my opinion. I would introduce a rule that, unless you have lived in the country for five years, then you cannot play for that country.

"Aiden McGeady should not be playing for the Republic of Ireland. If he had lived there for five years, that would qualify him. But McGeady didn't have an identity with the Republic of Ireland – his grandfather did, but he hasn't. Aiden was born and bred in Glasgow and he should be proud to play for Scotland.

"You need that siege mentality in international football. It is 11 Scots out there playing for Scotland, and you hear Flower of Scotland and you feel that identity. You think, 'I was born here, I was bred here'. Aiden McGeady will not get that feeling going to play for the Republic of Ireland. Nor will James McCarthy, a young Scot who took a similar route. This is wrong, totally wrong. And these English guys coming up to play for Scotland is also wrong."

Shiels doesn't mind being told he  has an old-fashioned view of nationality and a modern society's complex ethnicity. Indeed, he once sacrificed his own job-security because he believed that Fifa, via the grandparent rule, had besmirched international football.

"When I was a Northern Ireland youth coach, I was asked to play English players in my team. I said to Nigel Worthington [then the Northern Ireland manager]: 'Nigel, I'm not going to do this.' And I put it in my last match programme that I wasn't going to do it. In my eight years with the Irish Football Association, when we had a lot of success at youth level, not once did I use a 'grandparent rule' Northern Irish player. I stuck to my principles. I just said 'no'.

"Let me use this example. Suppose in Scotland you have a good kid from Falkirk who goes through the youth international teams, maybe starting at under-12s, under-15s, under-16s, under-19s. And let's say he plays right-back. All of a sudden Billy Stark, or some coach, is told there is an English guy from Huddersfield, who qualifies for Scotland, and he comes up and plays instead. The wee guy from Falkirk, having come all the way through the system, is suddenly left out. What message does that send out?

"Where is the identity with the Phil Bardsleys of this world with Scotland? I'll tell you: there is no identity. None at all. That is why international football is losing its top billing. It has been diluted. And it's totally wrong."

Shiels is thoroughly likeable, in part because he is a man of conviction. That mental strength also explains why he has emerged from relative poverty, setback and obscurity to make his way in football.

He suffered a horrendous injury when he was 15 which robbed him of a playing career in England. From his extraordinary family, he also had a brother, Dave, who was killed by the IRA. And amid it all was a towering father, Roy Shiels, a football-daft chicken farmer who left quite an impression.

"My father was my biggest influence," Shiels says. "He started having his family: George, then William, then Ian, then me. That was four boys. Five more would follow: Dave, Russell, Roy Jr, Sam and Amy. We lived in Maghera in South Derry, which was a bad area of Northern Ireland during The Troubles. My dad was a real character in the town and he ran a kids football team during those bad years of '72, '73, '74 when The Troubles were rife.

"Maghera back then was a totally split town: at the top lived Roman Catholics, at the bottom lived the Protestants. We lived outside the town, on a chicken farm, at the bottom end. The two communities didn't mix but my father was one of those guys who would just go into both pubs – Catholic and Protestant – and announce: 'My No.4 son has just been born. I'm getting there, lads. I'm building my own football team.' He brought Catholic and Protestant kids together, and they happily mixed in his football environment, away from their schooling. I developed Catholic friendships over the years and so did my friends.

"Everything was football for my dad, and he totally shaped my life. He'd come back from the pub on a Saturday night and put floodlights up in our yard, and we'd go out and play football after Match of the Day had been on. My dad had a great community spirit and sense of connection about him. He was a broad-minded man, and I think I've inherited that. I'm a tolerant person."

Early on, though, Shiels learned how to fight his corner. He had to, given the chaos of his upbringing, and has continued to do so this season after comments he made about officials got him into trouble with the Scottish Football Association. "That was a big thing coming from my background – fighting for yourself," he says.

Growing up amid all this, when Shiels, at 15, had his future football career taken from him, he knew then that coping with adversity would shape the rest of his life. He made a choice: either face it down, or melt away.

"It sounds immodest, but the fact is [that] there were lots of clubs after me when I was 15, before my accident," he says. "I was already in the Coleraine squad at that age and Aston Villa were after me. I was said to be the next big thing from where I lived. But at 15, in a cup game, a guy came in and whacked me – he tore my ligaments and damaged my tendons and it all got distorted. I didn't look after the injury. Back then sports science was primitive and physiotherapy was a sponge and a bucket of water."

His adversity probably explains why Shiels appears set apart from other Clydesdale Bank Premier League managers, most of whom he says he gets on well with, even if his opinions forever appear to be getting someone's back up. "I think I might be unique among coaches in that I got my badges right up to elite level by paying for it all myself," he says. "In most cases the guys are supported by the PFA, but I wasn't, because I didn't play professionally. So I've had to do it the hard way.

"If you look at Steve Lomas, who played for Manchester City, or Terry Butcher, a former captain of England, or Neil Lennon, who played for Celtic, it is so much easier for these guys to get a job because they played in the professional game. I'm not knocking them; guys like Terry have done phenomenally well this season. But these guys have got jobs because of who they were. I wasn't 'a name' so it was much harder for me."

Shiels has transformed Kilmarnock, energising their style of play, producing an intelligent team, and of course winning the 2011 Scottish Communities League Cup. At 56, what ambition is left? "The truth is, I haven't got much money in the bank for my family," he says. "I'm not going to earn much money at Kilmarnock but that doesn't mean I don't want to stay at the club. I'd love to stay at Rugby Park and develop the club.

"Everywhere I've been I've tried to leave a legacy. This is maybe self-praise, which is not to be recommended, but I was three years as head of youth at Tranmere Rovers and I feel I left a legacy there. That club is flourishing, as did Coleraine and Ballymena after the work I did there. So I'd love to develop Kilmarnock likewise.

"But any manager is just two bad  results away from disaster, so what's the point in talking of ambition? I just want to try to be as successful as I can be."