As rock stars they were as unlikely as they come. A pair of denim-clad identical twins from Auchtermuchty, armed with thick-framed glasses, acoustic guitars and booming voices. But after 25 years, it seems we still can’t get enough of The Proclaimers.

Emerging into the gaudy neon and day-glo-lit 1980s pop scene, Craig and Charlie Reid couldn’t have looked more out of place. But their simple honesty, harmonies and good old-fashioned songwriting endeared them to a nation. And to those who saw them, belting out their debut Letter From America on Channel 4’s chart show The Tube, and sporting tight jeans on Top Of The Pops, they were a revelation. And we still love them as much.

“I am proud we are still making music today,” says Craig — the oldest of the twins by half an-hour. “I am also proud that we have done things the way we wanted to and haven’t made any compromises.

“And after 25 years it’s great to still have an audience. We had a long period where we didn’t do shows or albums but we came back and still had an audience. But our audiences are now bigger than they’ve ever been.”

Craig comes across as gruff but modest. He clearly doesn’t suffer fools, yet despite a hectic touring schedule is polite and thoughtful, considering his answers carefully. He is clearly one of rock’s nice guys. “You have to be out there all the time,” he says. “And that means playing festivals.”

As the ultimate feel-good band, they are, of course, the perfect ingredient for a summer’s day of live music in a field. On Saturday they make their latest al fresco outing on the clipped lawns of Great Tew Park, where they will be delighting crowds at the Cornbury Festival. The show comes a week after their raucous singalong set on Glastonbury Festival’s Acoustic Stage.

“We had to leave soon after we came off stage,” says Craig. “We wanted to see The Rolling Stones, as we’re big fans, but if we’d stayed, we wouldn’t have got away ‘til 3am, and we had a show in Poole the next day.”

In fact it was Jagger et al who inspired the brothers to perform in the first place. “I’ve loved them from the age of 11,” says Craig. “I especially like their early stuff. They were a big influence. Hearing them was when we decided we wanted to play music — and we haven’t been able to shake it off. From then we just hoped someone would listen to what we were doing.

“We played for many years in different bands, and even as the Proclaimers, before we got any recognition.”

Their break came when they were chosen by The Housemartins to join them on tour. Letter from America reached Number 3 in the charts, while their album This is the Story went gold.

And, even now, after nine albums, he admits he can’t believe his luck.

“When we first started we were very poor,” he says. “Fortunately punk came along and we were able to play music without being able to play anything. After that we tried something different and progressed — ending up with just two of us, which meant not having to compromise.”

He has not lost sight of his roots and remains grateful to fans for helping him out of poverty. “I was unemployed for six years,” he says. “There were a lot of other people who didn’t make it and had terrible lives since then, so I thank my lucky stars.”

Was it really luck? “Some was luck,” he says thoughtfully. “But you make your own luck to some extent and have to stay motivated.”

To celebrate their first quarter of a century the brothers have released a 30-track compilation charting the story so far. The Very Best of The Proclaimers (25 Years: 1987-2012) has been compiled by the brothers. Craig insists the time was right for an update. “We did one in 2002 but since then we’ve had five studio albums,” he says. “We wanted it to reflect 25 years and took stuff from the early albums and mixed it into the right order so it’s like a live show.

“If you haven’t seen or listened to us live, there’s a lot more songs than you’ll remember. There’s a good balance too. We have done nine studio albums though, so most we’ve had to leave off.”

And which is his favourite? “Sunshine On Leith,” he says without hesitation. “It’s the most complete song we’ve done and the peak of our live shows for most people.”

It carries particular significance to Craig; the song is the club anthem of his beloved ‘Hibs’ — Hibernian FC — where he faithfully joins his old pals for home games.

So how do these avowed supporters of the working man feel about performing in the playground of the rich and famous — a festival where David Cameron is likely to drop in at any time, and where his riding buddy, the ex-boss of News International, Rebekah Brookes, and former spin doctor Andy Coulson have been spotted hob-nobbing? After all, the Reid bros have made no secret of their left-leaning politics and support for Scottish independence.

“Most of what we do is political,” says Craig. “But the message is in the music and in the songs and I’m happy to play to everyone, whether Tory or not.

“I wouldn’t vote Tory to save my life but if the Prime Minister wants to go to a festival in his own constituency, he should be able to do that.” So don’t expect any Elvis Costello-style rants about attacking Tories, which caused a frisson at last year’s event.

“People are not just there to see you at a festival,” he says. “They are there for everyone, so it’s really good if you can get through to them.”

So how do they prepare the set list? “Through trial and error,” he says. “We know what works and rotate songs. We never play the same set twice. It’s good to keep a certain danger and not do it on autopilot.”

And does he have any tips for festival virgins? “If it’s raining, take your wellies, and if it’s sunny take suncream. And keep drinking... alcohol and water!”

  • The Proclaimers n Cornbury Festival n Saturday n Tickets from Cornburyfestival.com or on the gate.
  • The Very Best of The Proclaimers (25 Years: 1987 -2012) out on EMI Records.