Going the distance: The Proclaimers on 25 years of singalongs, staying true to their roots and proving the doubters wrong

They were told by record label after record label that they’d never make it if they didn’t turn their backs on their distinctive brogue. But, with a greatest hits album in the can – and a movie in the pipeline – the Proclaimers have had the last laugh.

It was, you might say, Kevin Rowland's fault. Certainly he made the connection that confronted Craig and Charlie Reid with an inconvenient truth.

"Kevin introduced us to a music publisher in London," recounts Craig, the younger (by 30 minutes) Proclaimers brother, of the help the Dexys singer gave them as they attempted to progress their music career in the early 1980s. "And he was one of the guys who said, 'Look, the accent will be a problem.' He didn't say change it, but he said our accents would be an issue. And he was probably right. He probably still is right. But we were always gonna do it our way."

And so Craig and Charlie Reid wrote "Throw the 'R' Away". "Ah've been so sad/ since you said ma accent was bad," blared the Scottish twins over furiously strummed guitars and with furiously rolled r's, "he's worn a frown/ this Caledonian clown/Ah'm just gonna have to learn to hesitate/ to make sure ma words on your Saxon ears don't grate/ but ah wouldn't know a single word to say if ah flattened all my vowels and threw the 'r' away…"

Against expectation – gangly, speccy twins? Singing harmonies in strident Scots? Playing politicised folk music? In the poptastic early 1980s? The Proclaimers did secure both a publishing deal, and a record deal. Released in 1987, "Throw the 'R' Away" duly became their first single. Of course it did. A declaration of intent. A righteous singalong. A soapbox anthem grounded in proud, pragmatic defiance. And 26 years later, it's the first song on their new double album, a 30-track greatest hits marking 25 years' recording. Of course it is. Yes, agrees Craig, "Throw the 'R' Away" is pointedly the set's opening salvo.

"It's still one of the songs I'm most proud of. It's unique – I've never heard anyone write a song like that," he says. He's not being bumptious – just plain-spoken, as he and Charlie always are, both in conversation and song. The Proclaimers don't do mealy-mouths nor compositional platitudes. "And it was basically after us going to publishers and record labels, and hearing the same thing every time: folk saying, 'We like the songs but the Scottish accents – we can't do anything with that. That's gonna stop you doing anything.'"

A quarter of a century later, the writers of deathless hits "Letter from America" and "I'm on My Way" are still having the last (heavily accented) laugh. Six years ago a new version of "I'm Gonna Be (500 Miles)" was a nation-defining number-one hit in aid of Comic Relief. The Proclaimers remain a huge touring concern all over the world – the Reids are just back from an acoustic tour of America, where "I'm Gonna Be (500 Miles)" was belatedly a gigantic hit in the summer of 1993, courtesy of the soundtrack to the Johnny Depp film Benny & Joon. October sees the release of Sunshine on Leith, the feel-good film of the box-office-trumping theatrical "jukebox musical" named after their second album and written around the Reids' songs. The Scottish Mamma Mia!, if you like.

Last year's ninth studio album Like Comedy was buoyed by a hilarious video for the single "Spinning Around in the Air" directed by Little Britain star Matt Lucas, a lifelong fan. This year's Very Best Of… comes heralded by sleeve-notes courtesy of David Tennant – a fan so enthusiastic he got married to the Proclaimers.

"We Scots aren't known for our extravagance of emotion, but maybe that's why the passion seems to burst out of everything they do with an unruly abandon," says the Shakespearean one-time Doctor Who. "The rawness of the accents only adds to the rawness of the sensation. These songs have been with me through every day of the past 25 years: 'Joyful Kilmarnock Blues' was my teenage anthem, I walked down the aisle to 'Life with You'; every truly great night out I have ever had has included 'I'm Gonna Be (500 Miles)' at some point."

With "Throw The 'R' Away" kicking off the album, it's bookended with a new composition. "Not Cynical", premiered to great fanfare to Chris Evans' 10 million Radio 2 breakfast show listeners last month, shows that the Proclaimers' melodic bite and lyrical fire remain sharp and undimmed. "Glowing, how come you still look young?" asks Craig rhetorically, approvingly. "Fighting, life didn't get you yet…" Whom are these ardent socialists, Scottish nationalists and Hibernian FC fans, now aged 51, addressing?

"It's a number of people I know," replies Craig. "It's not any one person. It's people who've not let life grind them down. I don't mean people who are just happy-go-lucky or have no pain cos they've got no brain. I mean people who get the knocks that life gives you, but they don't get embittered. People end up getting blinkered as they get older cos everyone gets knocks. Some people, it cripples them. But I admire people who don't buckle. Who get knocked down but get back up again, and don't allow the past – whether it's mistakes or injustices done to them – to stop them focusing on going forward."

As it is in their heartfelt songs, this soulful positivism is imprinted in the proudly working-class Reids like a credo stamped through a stick of rock. It's there in "Let's Get Married", the lead single from their third album Hit the Highway (1994). It was even there in "Cap in Hand", a song on their 1987 debut This is the Story that questioned Scottish subservience to the British nation state. The Proclaimers don't do cynicism. OK, they do, on "In Recognition", their acerbic take-down of the honours system (which, again pointedly, is the lead track on the second disc of the new greatest hits). But mostly they don't.

"What pisses me off is injustice," says Charlie. "When you see people getting a shit deal for no reason. Some people bring it on themselves, clearly. But some people don't. That makes you question everything. I could never claim to have religious faith, but any belief I had in an Almighty is gone a long time ago. I don't dismiss the possibility of God, but in terms of injustice on Earth, the left were right: we've got to fight for it."

He smiles before reinforcing the point with feeling. "It's not going to be given to you. You need to fight for it. And you need to fight all the time, every day, or people treat you like shit."

They don't make pop stars like the Proclaimers any more. That's apparent, right? If you didn't know it from their songs, you'd guess it from the way they converse and conduct themselves. It's a sunny Friday evening in the heart of Middle England, and Craig and Charlie Reid are in Uttoxeter for the Acoustic Festival of Britain. Right now the twins are idling in a hospitality box in the grandstand at the Staffordshire market town's racecourse, waiting to headline the opening night of the small, three-day event. Their kit: one acoustic guitar, one tambourine, one penny whistle, two belting voices.

This summer they're doing a run of summer festivals, including Glastonbury and T in the Park. It's the first time they've played in the UK as an acoustic duo in a long time; for the past 20-odd years they've toured with a band, a rock'n'soul concern that amplifies (in every sense) the raucous party-with-a-conscience vibe of their shows.

But it's even longer since the twins last appeared in this part of Britain. Charlie recalls being here in 1987, playing with long-forgotten Anglo-American group Voice of the Beehive. It was in Burton-on-Trent, he says, "and was a venue that had been done up by the brewery or sponsored by the brewery. It looked like it had been freshly painted anyway. It was a small club – Craig reckons there were 40 people."

"It was 40," says Craig, flatly.

"I reckon 70."

"It was 40," repeats Craig.

"The first album was just out; was it just out?"

"Yeah," nods Craig with finality, the closing clarificatory note on a brief exchange that is typical Proclaimers. They might be brothers-in-arms-and-vocal-cords, but these near-identical twins with almost-identical belief systems are ever-ready to indulge in fraternal bickering. 'Twas, of course, ever thus, but even more so with siblings whose entire professional career and adult lives have been lived in each other's pockets (with eight children between them, both still live in Edinburgh, albeit in different corners of Scotland's capital).

One thing they agree on: in the audience that night were Bill Drummond and Dave Balfe. Drummond was later one half of the KLF, but back then had his own record and song-publishing company with Balfe, who would go on to sign Blur and be immortalised in the song "Country House".

The pair were but two of the eclectic bunch of early champions of this proudly "odd" musical act from north of the border. Drummond spent some of his childhood in Corby, the Northamptonshire steel town that was once largely populated by migrant Scottish foundry workers. Craig thinks that songs such as "Letter from America" – which drew deft poetic parallels between the Highland Clearances and the Thatcher-era destruction of Scotland's car and steel plants ("Lochaber no more… Bathgate no more… Linwood no more") – had personal relevance for Drummond. "The stuff we were singing about and the accents, they resonated with Bill."

"He was one of those people," adds Charlie, "that we clicked with right way – like Gerry Rafferty." The late Scottish singer/songwriter, a one-time musical partner of Billy Connolly and later famous (as half of Stealers Wheel) for "Stuck in the Middle with You", produced the band version of "Letter from America" that gave the Proclaimers their first hit (number three, 1987). Given their punk background (the teenage twins had been in argy-bargy bands in Fife in the late 1970s) and their no-compromise principles, did they worry that that re-recording was a sell-out?

"No, I didn't think sell-out," says Charlie. "But I thought: it's gonna be different. It was a necessary evil to get played on radio. Whether the punters would consider it a necessary evil, we didn't know. But we thought it was a natural progression. And so you wanted to put it in the hand of someone who would do a decent job. And we trusted Gerry with that."

Kevin Rowland was another ground-level supporter of the twins. He first met them when, as rabid Dexys Midnight Runners fans, the Reids bustled backstage at St Andrews University in early 1980. They became friends, and when they started performing as the Proclaimers, Rowland sent the unemployed pair cash to record demos.

"A couple of times he put money up…" begins Charlie.

"….50 quid," chips in Craig.

"…and once we stayed with him in Birmingham for about four days, and he paid for the whole thing," continues Charlie. "Really generous." When the twins received one of their earliest bits of media exposure, on Janice Long's night-time Radio 1 show, Rowland came down to lend support. "All the way through, from signing our record deal and beyond, Kevin was helpful."

Janice Long had already played a role in kickstarting the twins' professional career. When, in 1986, the Housemartins were guests on a Radio 1 single-review show hosted by the DJ, they put out a call to listeners: "Where are the Proclaimers?" The Hull band had been handed an acoustic demo tape by a Proclaimers fan at a show in Aberdeen; impressed, the equally socialist and soul-minded four-piece wanted the Reids to support them on tour.

Contact made, band-leader Paul Heaton invited the twins down to Hull. "It was one of those pivotal moments in your life," says Craig of his and Charlie's visit. They went on a pub crawl with the Housemartins, slept for a few hours in Heaton's front-room, then caught a bus back to Edinburgh. "And that was it," he says, "we'd got that tour. I don't think we would have got a record deal if we hadn't got that tour."

But that's enough of all that nostalgia. In 2013, the Proclaimers are all about looking forward; the 1980s revival circuit is resolutely not for them. There may have been family- raising longueurs between albums (six years between Sunshine on Leith and Hit the Highway, then seven years till their fourth album, 2001's Persevere) but they never split up and never really went away. Don't call it a comeback, not least because the feel-good smash-in-waiting Sunshine on Leith movie – directed by former actor Dexter Fletcher, produced by Andrew Macdonald (Trainspotting) and starring Peter Mullan and Jane Horrocks – is only adding spurs to a career with its own restless momentum. As evidenced by the cheers and dancing and singing that attend the pair's exuberant Uttoxeter show later that night, the Proclaimers are very much a going, roaring concern.

To the question of whether they still feel hungry, Craig and Charlie answer in quicksmart unison: "Aye."

"I still feel the best songs and the best performances are yet to come," Charlie elaborates. "I think you've got to feel like that. And you're aware of that – we were 51 this year – of how long will you keep your health, how long will you be able to do it? You've got to look after whatever talent you've been given, guard yourself from too much excess. And keep working. And realise it will come to an end. So you better try and make the next record the best record. Cos it absolutely will come to an end. That's one thing for sure."

Do they consider themselves a soul act? "I wouldn't say we're soul," says Craig, who will start work on writing a new Proclaimers album with his brother this autumn, once their international touring obligations are completed. "But there's soul running right through everything we do. I think we're an intense act. I think we're an intense act," he repeats. "Yeah, I think we're an intense act." If a point's worth making, it's worth making three times. More power to the Proclaimers and their impassioned rigour.

The Proclaimers' 'The Very Best Of: 25 Years (1987-2012)' is out now