"Some of these musicians take themselves so seriously," adds Andrew with a groan. "They walk on stage as if they're clergy, with no shoes on or something. Everyone's standing worshipping them, but it's not folk music when the stage is so much higher than people's heads.

Anyone who has been to a Mary Wallopers gig will know precisely what they're referring to, but their word-of-mouth nature and existing views of Irish trad music mean it's been easy to miss them, no matter how meteoric their rise. They may be near enough selling out two nights on the bounce at Brixton, but their determination to forge their own path means it can be hard to slot them in with other bands, even those who – like them – are embracing their Celtic roots. In part, this is down to sheer bloody-mindedness, but it also comes from their origins in Dundalk, a border town in Southern Ireland which is about as culturally distant from central Dublin as it is from misty-eyed images of rolling hills and turf.

"People have a healthy cynicism there, which is good," adds Andrew. "You can't get too many notions about yourself. There's a disrespect for authority, too – everybody knows someone who does a bit of smuggling or dodgy dealing. Everyone likes a bit of dodgy craic in Dundalk, which suits us down to the ground," he says with a laugh.

Despite this industrial history and the unique culture it, and the town's border location, have left behind, Dundalk's economy has taken a beating over the past few years, with the tech firms who have flocked to Ireland only widening the disparity between the country's richest and poorest citizens. The band's well-deserved anger at the situation finds its way into their songs, with the lyrics of 'The Idler' imploring people to focus on the real villains and to "blame the idler who forgets their history / And says "Ireland is full, I'll look after our own".

"We had a recent election in Ireland," explains Andrew. "And a huge amount of people our age didn't vote, and all the right-wing cunts said it was because we didn't care, but it's because everyone my age or younger have been driven out of the country because they can't afford to live in Ireland. They're in Australia or Canada because of the policies of those people. It's disgraceful that because of the rent crisis and austerity and everything else that Fianna Fáil and Fine Gael [Ireland's two dominant political parties] have created, we can't even change it because we're all being forced to emigrate."

"But it really is our culture," says Charles. "It's in our culture to be an immigrant. A lot of the traditional songs are about dreaming about being in Ireland because they were written by immigrants. That's why it's so frustrating, the thought of Irish people turning around and falling for the same bullshit about refugees that we were subjected to in England for so long. Irish people were forced to sign anti-terrorism waivers to get into the country, and the amount of innocent Irish people who were put in jail or questioned or beaten up by the cops for being in the IRA when they never were – how can people forget that so quickly?"

It's heavy stuff, but it's a far cry from the drunken revelry of a Mary Wallopers gig, a contrast which is completely intentional. The band play a set consisting primarily of reworked covers of traditional songs rather than originals, and aside from the Palestinian flag draped over part of the stage and some between-song banter, contemporary issues aren't pushed to the fore. Far from sidestepping an issue so big it can feel paralysing, though, this is just a different way of approaching the subject on the band's part.

"It's as simple as that." agrees Charles. "We try to use our platform to raise voices where we can, but really our biggest tool is getting these ideas across through quite nostalgic songs, because they're ideas which have always been there.

Whatever the topic, both Charles and Andrew eventually bring things back to the live experience. It's not surprising for a band who cut their teeth doing pub sessions in return for free beer, but two albums in, it's an attitude which has started to shift ever-so-slowly. Debut 'The Mary Wallopers' and follow-up 'Irish Rock N Roll' were released within a year of each other, and both consisted mainly of traditional songs reworked by the band. While they more than hold up as albums in their own right, you can tell they were a reflection of the band's gigs rather than the other way around. Album three hasn't come so fast, and when it does, it's likely to be a very different beast. The changing direction of the band was accelerated by founding member Sean McKenna amicably leaving the group in March, with the remaining members keen to try something new.

"The first two albums are a snippet of what we do live, but this one will be more experimental," says Andrew. "We want to spend some time on it and mess around with it, rather than, like, take two weeks and just fire it out.

And if it doesn't work out? Well, they aren't exactly worried.