No offence to Scotland's reigning kings of twang-happy folk-rock, but if David Lynch ever made a documentary about The Proclaimers, he would surely have to call it "Twin Geeks".

Behold Auchtermuchty's answer to the Everly Brothers. With their accents and specs both super-thick and their checked shirt/ jeans wardrobe combo seemingly inspired by the rodeos of Planet Nerd, twin brothers Craig and Charlie Reid have been the butt of endless jokes over their 30 year career.

But so what? They couldnae give a toss, Craig tells me down the line from Edinburgh. Hell, they even had a few laughs themselves when their 1988 single (I'm Gonna Be) 500 Miles conquered the world.

Murdo MacLeod Shall we take them for a wee walk up to Edinburgh Castle? The Proclaimers in their home city.

"That song is by far the biggest thing we've ever done," says Reid. "It's bigger than all the other songs we've done combined, and bigger, even, than The Proclaimers itself. 500 Miles is a monster all over the English speaking world. It's bought us a couple of houses, that song!"

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He wrote it in under an hour. "We were waiting to head up to Aberdeen for a show, so I sat down at this little electric piano and I got it straight away. It just came - the chords, the words, the whole thing just fell into my lap inside 45 minutes!"

Murdo MacLeod Craig and Charlie Reid in Edinburgh, with four Scottish deer hounds fresh from the Cairngorm mountains.

That stomp-along ballad has since become a bona fide anthem, and with good reason. Work, travel, love, loneliness, growing old, talking rubbish, drinking too much - it's all covered in that song.

No wonder it's now sung with great vigour by pissed Australians and Austrians, Brits and Yanks, Kiwis and Canadians, many of whom are only too happy to temporarily adopt fake Scottish accents.

"Aye, but I think that's alright, you know? People are just showing their affection, really. It's a very unusual sort of love song because the beat is a kind of march, but that's helped it become a favourite drinking song. It sounds great, belted out in a pub. And it gets played endlessly at sporting events all over the world. It's a f***ing huge anthem in ice hockey games, for God's sake!"

Murdo MacLeod Sunset on Leath: The Proclaimers on their home patch.

He laughs a little too long at this, to the extent that I suspect there might be whisky involved. I picture a nice peaty single malt at his elbow, gleaming golden in a heavy glass. A Laphroaig, perhaps, direct from the Isle of Islay.

He laughs even more when I mention the confusion 500 Miles has generated over the years. Not only did the brothers dare to deliver the thing in their own broad brogue, they chucked in a few Scots words as well.

Case in point: haver. As in "If I haver, I'm gonnae be the man who's haverin' to you!". All over the world, heads were scratched.

"Aye, well, haver's a word people in Scotland use all the time. It means to blether any old rubbish, to talk shite. If you're drunk and makin' no sense, people will say- ' you're haverin' shite, son.' It's the only real Scots word in the song, but people have asked us about it for the last 30 years, especially in America. One guy asked us if it meant vomiting. Someone else thought it had sexual connotations."

And I think Reid and I have been haverin' about just one song for far too long, given that this is a band with an impressive back catalogue. 500 Miles might be their biggest ballad, but it is not their best.

Their three decades together have yielded ten albums so far, including the last year's well-received Let's Hear It For The Dogs. Every album has mixed country/ soul-inflected love songs with more forthright political material, with a few rougher rock tracks that betray their past in punk bands.

What were these long-forgotten punk bands called? He's not telling. I suggest a perfect name would have been "Eight Eyes", but it seems Reid hasn't drunk quite enough whiskey to appreciate this particular joke.

Alongside their own recordings, the duo's songs also inspired a stage musical, Sunshine On Leith, which was adapted into a movie in 2013. Their audience continues to grow with every tour. And now, for every sour soul determined to write them off as some sort of porridge-fuelled novelty act, there are a hundred others who love them with great ardour.

Former Dr Who actor David Tennant once bent my ear for an eternity over the duo's brilliance, thereby chewing up half of our allotted interview time. And Little Britain's Matt Lucas is another huge fan.

In the liner notes to the band's 2013 Best Of collection, Lucas writes: "I find it hard to put into words quite how the music of The Proclaimers makes me feel. It makes me laugh. It makes me cry. It just makes me generally euphoric. Sunshine On Leith says more to me about my life and the way I feel than anything Morrissey or Cobain ever wrote."

To my ears, their greatest song is Letter From America, from their debut album, This Is The Story. It came out in 1987, when I was living in Edinburgh myself, the brothers Reid practically neighbours, with me living at the top of Leith Walk while the twins hailed from the bottom of the hill, near the port.

Letter From America had a deep impact when it first came out. I regularly witnessed a room full of Scots singing along with tears in their eyes. In pubs, at weddings, in damp basement flats, a few bevvies and this song would soon be getting sung, and the emotion in the room would rise up and spill over like froth from a shaken beer.

It's a song about loss and leaving and family ties stretching thin, a love song to one's home soil. Its themes are displacement and emigration, with wave after wave of Scots forced to leave to their homeland and start new lives in America and Canada.

Lochaber no more. Sutherland no more. Lewis no more. Skye no more. The chorus tells of towns emptying out as able-bodied young men head off to build Chicago and New York, or toil in the "New Scotland" shipyards of Nova Scotia.

"That song was inspired in part by the de-industrialisation of Scotland, South Wales and the north of England," says Reid. "You suddenly had massive numbers of jobs in heavy industry being lost almost overnight. In the steel industry alone, there were 50 000 jobs lost in just two years! It was an economic and cultural catastrophe."

All of a sudden, everyone was either on the dole or leaving the country. "It struck me that none of this was new. There were strong parallels with the mid 19th Century during the Highland Clearances, where working people were cleared off the land to make way for sheep that would make more money for wealthy landowners. They either moved to big industrial centres in Scotland or they went to Canada, the US, New Zealand, Australia, South Africa- wherever they could find a new life."

Scotland's shattered economy has yet to recover. Reid himself spent over six years unemployed during the early 80s, a time when he and his brother scratched by on the dole while working on their songs.

"I've never shaken it off, actually - that feeling of being a young person who's not in control of your own destiny. The fact that this was allowed to happen for hundreds of thousands of people really got to me. That rage has never left me, and you can hear it in a lot of our songs."

Say it loud! I'm Scottish and I'm proud! You also hear a strong regional accent at the forefront of every track, and the band started doing this at a time when such cultural confidence was unusual, with bands all over the UK trying to sound like they came from London, or worse still, America.

"Well, there was no way we were gonnae sing about our own experiences in our own country in somebody else's accent. That decision has probably limited our career in some ways, but also makes us more distinctive. Both Charlie and I came up through punk bands, and just like punk, our music was about individuality and expressing yourself in your own way."

Born in Leith in 1962, the twins grew up in Edinburgh, Cornwall and Auchtermuchty. They were weaned on their parents' favourites - Jerry Lee Lewis, Merle Haggard, Hank Williams - and started playing music together at the age of eleven.

"We were influenced by 60s stuff by The Beatles, The Stones, The Who and the Kinks, and then punk came along and changed everything. It was just three chords, fast as hell and badly played, and it was so inspiring! It showed anyone could give it a shot. We became obsessed with the Pistols, The Damned, The Clash and The Jam, and they inspired us to make the music we liked, no matter what."

They started calling themselves The Proclaimers in 1983, and just kept trudging away, playing wherever they could, desperate to get a break. I imagine this took a great degree of self-belief and perseverance, given that the brothers do not look like traditional pop stars.

They are, in fact, almost extravagantly unsexy. Even 30 years ago, when they were fresh-faced young men just starting out, you couldn't really imagine them smiling down from glossy posters in the bedrooms of teenage girls.

"That's true, but like our accent, the way we looked just made us more distinctive. People might think we look like arseholes, but they remember us, you know?"

If anything, looking so nerdy worked to their advantage. The twins were so used to bemusement and hostility as kids, it hardened them up for anything that came their way later on.

"Any insults people might throw at us now are like rain off a duck's arse. We could'nae care less. We grew up in a very ordinary working class house and went to a wee state school where we were in the same class, wearing the same big specs, in a place marked by failure and poverty. We couldn't go under the radar, because if you're twins, people are always looking at you, or shouting stuff at you from passing cars. Any insult that was ever gonnae come our way, we already heard it when we were kids."

Their breakthrough, when it came, was a bolt from the blue. The brothers sent a demo tape to British music TV show The Tube and were invited down to Newcastle soon after for a televised performance that was broadcast live nationwide.

"Straight afterward, we caught the train back to (Edinburgh's) Waverley Station and then walked home up George Street carrying a guitar, and all these folk shouted out - 'I just saw you on telly the night!' It was unbelievable! There were only four channels in the UK at that time, so every young person interested in music was watching that show. Everything took off from there."

They were on their way, from misery to happiness that day. "Ha! Yes, indeed we were, and we're still on that same road. We've made ten albums now in 30 odd years, and this will be our fourth time in New Zealand, I think. At the age of 54, we're better singers now than when we started out, and I think the songs we wrote last week are as good as any of the early stuff."

Bathgate no more. Linwood no more. Methil no more. Irvine no more. The villages of Scotland are still emptying out, albeit at a far slower rate these days, with the young and ambitious seeking greater opportunities in London, Los Angeles, Dubai, Berlin.

But the Reids remain in Edinburgh, an easy stroll from the suburb of their birth. Is it likely they would ever leave Scotland to live somewhere else?

"I wouldn't think so, no. We travel a lot, but be both love Scotland, Edinburgh especially. Despite the cliches people come out with, I think people are highly individualistic here. We had to fight hard to keep our liberty and our identity, and we're still fighting for that, really. People in the south of England often portray the Scots as really contrary people, always with a bee in their bonnet about something. And we write them off as smug as f***, without enough trouble in their lives to build much character. Really, we Scots have more in common with people from the north of England, or Ireland, or Wales, I think. But The Proclaimers is a band, first and foremost; we're not trying to be some sort of Scottish role models. We are who we are, and we just happen to be Scottish."

The Proclaimers play Wellington April 22; Christchurch April 23; Hamilton April 24 and Auckland April 25.