For Robert Plant, collecting his first ever clutch of Grammys in 2009 was a moment of vindication. “Every time we went up to the podium, I kept seeing Coldplay start to stand up,” he told Vanity Fair recently of the night that the 2007 covers album Raising Sand swept up all five awards it was nominated for, “and I’d say, ‘Sit down! My turn! F*** off!’” Alison Krauss – his collaborator on the record and a Grammy veteran, having previously bagged 21 over a celebrated career in bluegrass and country music – on the other hand, was distracted by urgent problems developing beneath the surface.

“I was mostly concerned with my undergarments, under what I was wearing,” she laughs down the phone from her Nashville home. “That was a lot of work. Haha! That’ll really keep you occupied, that whole process of trying to keep everything in its rightful spot. I do remember walking backstage trying to adjust all kinds of things and [Robert] was like ‘come on now’… but he had a very nice night and it was fun in that, but the undergarments were unfortunately taking a lot of my attention.”

If this makes Plant and Krauss sound like an old married couple out for an anniversary treat, it reflects the obvious, natural musical connection between these two revered figures from across the cultural divide between roots and rock. Raising Sand, reinventing 13 lesser-known gems from the annals of blues, country and Sixties pop handpicked by producer T Bone Burnett, was a rich and evocative marriage of Plant’s earthy blues impetuosity and Krauss’s sumptuous bluegrass precision, the grizzled rock mystic bringing grit to the polish of the pristine country queen. And 14 years on, their repertoire once more in the hands of Burnett and many of the same Nashville players, they’ve repeated the trick.

“It really felt like we’d probably record again,” Krauss says of the lengthy gap between Raising Sand and the pair’s equally noir and engrossing new album Raise the Roof. “I didn’t know when and you don’t want to force anything or do things out of time. Those timelines of things, you don’t always know why they are the way they are. I wasn’t sitting around, and neither was Robert, going, ‘hmmm, I wonder why we’re not…?’”

Following their 2009 Grammys success, Krauss explains, the pair did reconvene in a studio to start early work on a follow-up, but after three years of working on Raising Sand, recorded in 2006, a break was in order. Other projects – Krauss with her band Union Station and Plant with the Band of Joy and the Sensational Space Shifters – intervened; the break became a decade.

A fortuitous collision on the same bill at Willie Nelson’s Outlaw Festival tour in Indianapolis in September 2019, though, brought them back into each other’s sphere, and the songs came easily. A shared love of Calexico’s “beautiful and meaningful” borderlands groover “Quattro (World Drifts In)” sent Plant back to Nashville to rekindle the old spark.

“With Alison and I, we’re leagues apart in so many elements,” he says from his home on the Welsh borders, “and then when you realise it, that’s part of the magic of the whole thing. It comes from our continued surprise at how we can twist songs round and round. It’s never really appropriate for the limitations of my voice, some of the country stuff that we have touched on, but when we get it right, and the right key to sing in for the both of us… it’s just so surprising. When we sing we just look at each other and laugh.”

It’s not just a wrought-in-heaven synergy of voices that’s key to the Plant/Krauss charm, although that remains wonderfully evident as they reimagine The Everly Brothers’ upbeat “The Price of Love” as a seamy alcoholic’s lament or dig into the darkness at the heart of Ola Belle Reed’s gallows ballad “You Led Me to the Wrong”, Geeshie Wiley’s creeping voodoo junk-rag “Last Kind Words” or Aubrie Sellers’s hardship rocker “Somebody Was Watching Over Me”. It’s also their love and respect for the material – even as they lure much of it out into the depths of some dusky bayou – and each others’ roots.

Krauss recalls their first conversation, at a Leadbelly tribute Plant had invited her to play with him in Ohio in 2004; Plant waxed lyrical about a “mysterious, beautiful” album by bluegrass banjo legend Ralph Stanley called Clinch Mountain Gospel, a key text amongst Krauss’s bluegrass community. “He talks about listening to the record in the Seventies, driving through the Appalachian Mountains,” she says, “ because he was so mystified in general about his musical life, and in the music that came out of a certain region. To hear him bring up our people was really moving… I came home after that trip and my brother said ‘what’s he like?’ and I said ‘he’s like us.’”

Was she daunted to meet him at all? “No, not at all. I was surprised. I didn’t have any idea what he was like, I’d seen him on MTV in the Eighties and loved my own part of growing up with new music from him. My brother and I loved ‘Big Log’, we thought that was stunning. I was surprised at what a genuinely kind and generous person [he was], and a joy to be around… He’s a very generous, kind person. You hear that someone lights up the room but that really is a true statement for him.”

On Plant’s part, he appreciated the closeness of the bluegrass world. “It’s family,” he says. “They’re a tight family, and I appreciate all of that. There’s something about coming from a sturdy root… there’s a charm that it exudes.”

“We’re from two different worlds, but it’s a very pleasant incompatibility,” Krauss says of their connection. As such, both albums, they agree, were mutual learning experiences. “You can hear what I learnt,” says Plant, “I learnt how to apply myself to songs where the vocal is so naked… There’s no primal screams, you’ve just got to tell the story.”

Krauss, meanwhile, learnt to step outside the regimented perfectionism of bluegrass music. “You have to sing the same way every time or people get mad,” she explains. “They’ll kick you out. You have to because somebody’s gonna be left hanging out there. That’s family harmony… it’s really detailed. With Robert, his whole existence, he’s an off-the-cuff singer, he sings it differently every time. That is such a beauty of it and why there’s such a relationship with the crowd. It’s designed for them that night, someone’s gonna play it different on the guitar, he’s gonna sing it different, and it’s stunning.

“I’m used to doing things a thousand times [but] I really got reminded what we’re doing when I would watch him sing. We’re capturing this moment in time.”

Having captured some moments around Nashville between sessions too – Plant would hit the 3rd and Lindsley club on a Monday to catch fiddle trio The Time Jumpers but avoided the city’s famous downtown Music Row of country bars because “my liver couldn’t take it” – the pair completed Raise the Roof in the nick of time, just before lockdown in 2020. The isolations of the past two years, while undoubtedly difficult, seem to have suited them both. Plant has spent much of his time “in a shack on the side of the river on the Severn”, excavating archive cassettes of unreleased material to be made public only after his death, revisiting his career on his podcast Digging Deep, learning more Welsh and becoming “really handy at looking after trees and wandering around like a kind of poor man’s Robert Macfarlane”.

Lockdown also allowed Plant to “revisit and justify myself in my obsession with music”, returning to indulge in the pivotal moments of his personal sonic evolution. He rediscovered the excitement of his earliest musical awakenings – “the concussion of finding America, pre-Led Zeppelin… the glamour of the early to mid-Sixties, which was when I was a kid at school and some great Dion DiMucci moment had transcended into The Strawberry Alarm Clock and 13th Floor Elevators and all that sort of stuff”.

It’s given me a lot of spirit and heart, and also a whole different way of looking at the deal that I’m in

Robert Plant

He became freshly fascinated by the arrival of the earliest punk acts, “born out of a new generation taking things really back to basics” to challenge “the self-indulgence of the late Seventies”. And he took time to “explore the new worlds that I’ve found since I first went over to Nashville in 2005 or ’06”, specifically citing the under-appreciated work of Los Lobos. “It was another great revelation of how charming and magnificent these other great portals are as they swing open – it was endless, looking in there… It’s given me a lot of spirit and heart, and also a whole different way of looking at the deal that I’m in.”

The private and introvert Krauss, meanwhile, gained a fresh appreciation for her life as a musician: “You get wrapped up in the process of doing what you do and oftentimes you forget just how special it is.” But she also found herself fretting over the future of the bluegrass scene (“everybody mingles, it’s like a big family reunion every time you go out, and the pandemic takes an event like that and shatters it”), and America itself.

“That’s a very sad subject, the division in the country,” she sighs. “There’s such a romanticism with unity among the people and a lot of pride. We’re blessed to be able to have elections but to see such a lack of unity any more… I’m not trying to be a political person and I never talk about it, but there was so much division in every way.”

Plant tires quickly of questions on politics. Of Boris Johnson’s pandemic record he jokes: “I’ve watched a lot of Monty Python, put it like that, and I didn’t realise it was a new run!”, and on Brexit: “The whole place is in uproar right now, there’s a million errors and at the same time every day somebody somewhere brings us some light.” When asked for his thoughts on so-called cancel culture, he becomes defensive and dismissive. Is it a good thing that Led Zeppelin’s ‘rock’n’roll’ behaviour wouldn’t be considered acceptable today? “How can I even comment? It’s such an oblique question. We’ve been hearing it since the beginning of time, and who else does it apply to? What is going on? Is it footballers, politicians… some guy who’s just fixing his garage? For f***’s sake.”

Does he ever worry about the modern moralists of Twitter getting their hands on Hammer of the Gods? “How many times has that been round and round and round? It’s bullshit. It was written under a pseudonym, the whole thing is a fiasco… It’s a very old fable, and quite hackneyed I think.”

When considering what he learned about himself during the pandemic, Plant refers back to a 1975 car crash in Rhodes which left him wheelchair-bound. “I was off my feet, I couldn’t walk for seven months, and that was something to get used to because I’d always been pretty at it, soccer, tennis or just careening with madmen. So [again], what I found this time, in this remarkable situation, was that I didn’t really know who I was.”

In interview, Plant often discusses past versions of himself with some distance – “I don’t really know the guy who’s singing,” he told Vanity Fair of Zeppelin’s “Black Dog”, “I’ve heard a lot about him, but I don’t know what the hell his game was.” Does he change often with each stage of his life?

He laughs aloud. “Well I don’t really know what I’m doing now! That’s why I love it. It’s like one of those paintings you see and at the end you say, ‘hey, that’s a beautiful picture,’ and underneath it all there’s a bunch of numbers… I do look back and go, ‘Why? How?’ Of course. I started making records when I was 17 on CBS way back in ’66, so naivety is a magnificent thing when you look at it. It’s all about learning how you do what you do and living within it until you’ve got it right, and then just seeing something else and why don’t you just drive at it, go.”

We touch briefly on what was probably the most life-altering event for Plant, the loss of his five-year-old son Karac from a stomach illness in 1977. How does something so unimaginably devastating change someone? “Well, it makes you much more of a father than you thought you’d ever be for my daughter,” he says. “I did my best. I think as a family we have never gotten round that, never gotten over it.” Was that the end of the party? “Yeah. That’s the end of the statement.”

I was surrounded by the blue-eyed soul English singers who were royalty to me

Robert Plant

Do you struggle to understand the people you’ve been? “Oh, absolutely not. They’re all like little watercolours. When I was a kid, when I first started cutting records and going into Zeppelin and stuff like that, I was surrounded by the blue-eyed soul English singers who were royalty to me. So I was always wondering, ‘how am I doing? Is this the right way to express this song? Am I doing it right or am I just going back to type?’, or whatever. You think about the people that were around when we first put Zeppelin together, for all the madnesses and exaggerations, it was a part of the time that we were in and I really feel that we probably over-egged it a little bit, to say the least, but Jesus Christ it was very exciting… We were a law unto ourselves.”

The Robert Plant and Alison Krauss of 2021, now 73 and 50 respectively, don’t foresee quite such a monumental gap between their second and any potential third album together, following a tour for the album next year. Krauss reveals there has been “lots of talking, you never know! It has to be the right songs, so that’s what you wait for. If you get the right song… But I know everybody’s excited to get out and play, I’m excited and really proud of this record, I think we have something that’s really beautiful and representative of us at that time.”

One thing is certain – after far too long a wait, Plant and Krauss have once more proved themselves a duo of formidable alchemy. Maybe not raising the roof, but undoubtedly raising the bar.

‘Raise the Roof’ is out now