ROY Harper broke a long-standing habit recently. The singer-songwriter who was championed by Led Zeppelin, Pink Floyd and Kate Bush in the 1970s and 80s and has more recently been cited as an influence by a younger generation including Fleet Foxes and Joanna Newsome, has never been one for listening to his own records. Although songs would often remain in his live repertoire for years afterwards, generally speaking, once an album was completed, he moved on.

With the reissue on vinyl of three of Harper’s classic 1970s albums, Flat Baroque and Berserk, Stormcock and Lifemask, he was obliged to listen to the remastered versions and has reassessed at least one of them.

“For decades I'd regarded Lifemask as unfinished,” says Harper, who celebrates his seventy-fifth birthday year with a tour this month that includes his first concert in the Usher Hall, Edinburgh since 1969. “But of course that's silly because if I'd written and made every album a thousand times every one of them would in the same way be unfinished. It's the living record of an event, and a wonderful record at that. The drawback is that perhaps you have to listen to it a few times to begin to understand it, but perhaps not. From treating it as 'unfinished', I now think of it as one of the very best.”

Lifemask, with its side-long epic The Lord’s Prayer, and Stormcock, found Harper luxuriating in long-form songwriting, a fascination that stems from the influence of symphonic music, the Norse sagas and the one subject he liked at school, Shakespeare.

“Symphonic music is able to express mood changes in so many different ways,” he says. “I've never been attracted to opera because I think that, at the same time as voices like Pavarotti and Callas can obviously be very moving, it can also be quite stilted in its form and structure. I believe that opera could successfully be modernised. I think for instance that my Lords' Prayer or The Game could be adapted for different voices, although the adaptations would have to be scripted with changing visuals, dramatic pauses and perhaps narrative. The storyboards are there anyway.”

Soon after these records, Harper was leading a band, Trigger, something he wishes he could have had the money to pursue for longer, and flirting with the pop charts. Released as a single, One of Those Days in England made the lower reaches of the Top 50 and his evocation of English summers, When An Old Cricketer Leaves the Crease became a familiar radio track. He’s not a fan of social media and wishes people would stop posting his old TV appearances on YouTube but among clips from the Old Grey Whistle Test with the band are solo items from other programmes that confirm Harper’s ability to create a remarkably strong presence in his pomp with just his voice and his highly individual acoustic guitar playing.

As a teenager in the 1950s, like the rest of his generation of musicians, he was seduced by the skiffle boom in general and Lonnie Donegan in particular. Donegan led to the blues and the blues led Harper to “more or less 24/7” immersion in guitar picking.

“The world was a very different place when I first picked up a guitar,” he says. “Before Bill Haley and Elvis Presley, it was mostly light orchestral, the dying embers of Music Hall, popular songs by people like Gracie Fields, Frankie Vaughan and Vera Lynn and the local police band marching up and down the pitch at half time playing ‘Pack up your troubles in your old kit bag and smile, smile, smile.’ The most hip thing was Bing Crosby, soon to be followed by the young Frank Sinatra and the 'bobby socks' era. Lonnie Donegan hit Britain at about the same time as Elvis Presley in the mid-1950s and for anyone interested in the emotion of music at the time, Donegan was a bombshell. He was the real English Presley.

“We quickly went to the people who'd written the songs he was singing – Leadbelly, Big Bill Broonzy, Josh White – people who were making music which for us seemed to be from a different planet. It was an eye opener: real songs about real things sung by real people. We'd never heard anything like it. It was so moving. It changed our world overnight, a sledge hammer of a cultural change. A real and absolute revolution the like of which I haven’t experienced since. Most of the people who later founded rock and to some degree contemporary folk, started there, in that cultural moment. For lots of cultural, demographic and societal reasons that sort of thing hasn’t really happened since. It could, but an equivalent would be to suddenly hear music from outer space.”

Arriving in London from Manchester in the 1960s, Harper became part of the scene that included Bert Jansch, Davy Graham, all-nighters at Les Cousins in Greek Street, Soho, and eventually, via albums including Sophisticated Beggar and Folkjokeopus, the Harvest Records label, on which he not only recorded his own work but also sang Have a Cigar on Pink Floyd’s Wish You Were Here.

Like Bert Jansch, Harper was an acoustic troubadour with rock star admirers. They sought him out. He remembers Jimmy Page approaching him backstage at Bath Festival in 1970 and asking him to play the instrumental Blackpool from Sophisticated Beggar. Thanking the man who would shortly afterwards be celebrated in Led Zeppelin’s Hats off to (Roy) Harper, Page went off to play with his band. Harper thought the band were special but although they became good friends, his enduring impression was of Page’s trousers being too short.

At the time, although he too could sing of amorous liaisons (Another Day, with David Bedford’s beautiful string arrangement still sounds wonderful), Harper was channelling righteous anger into his songwriting. He still does.

“Yes, but it has to be real, and heartfelt,” he says. “My current favourite is Hangman. That people can even think about bringing back the death penalty is profane. Yes, some people deserve to be locked up forever, but they're the responsibility of society. They are part of what we are. We have to be able to civilise, to teach with heart, and to keep the savage in ourselves under scrutiny rather than allowing the mob in us to rule.”

Harper himself came scarily close to falling on the wrong side of the law in 2013 when following the Jimmy Savile scandal and Operation Yewtree, he was charged with committing a series of child sex offences in 1970s and was cited to appear in Hereford Magistrates’ Court, near his former home where the offences were claimed to have taken place. All charges were subsequently dropped but not before the singer spent all his savings – and more – hiring a defence team. Not surprisingly, he was very, very angry about this.

These days he lives ostensibly in retirement in Clonakilty, County Cork, where he’ll go down to the local pub and listen to traditional music sessions. He also listens to Miles Davis and Richard Farina when he’s not cultivating ideas that still spring from his responses to what’s happening in the world.

“Ideas are like food,” he says. “There's all kinds of them, and some are jotted down for use. Some of those don't make any sense the following morning, but others end up as lines in a song or poem, or lines in an essay. Some even end up as sayings in our house or are just left to grow old in one of the little black books I keep.”

He’s cryptic about the songs he’ll be singing on tour, on which he’ll be accompanied by a string and brass ensemble, citing but not naming “two from Stormcock, two from Flat Baroque and Berserk, three from Valentine, two from HQ, one from Lifemask, two from Man And Myth, and the rest to be thought about.” But he has fond memories of his previous Usher Hall concert, which was full of excited young people, he says. He also has strong memories of George, the chap who used to book his gigs in Scotland and apparently went on to be some kind of authority on camel dung, and of playing at a rally where miners leader Mick McGahey was whipping up the crowd and Harper founding himself standing next to a bloke who passed him a paper bag.

“It was like being offered some crisps from a packet, but when I looked inside they were mushrooms. I looked at the guy and he was about a light year behind a pair of specs. Taking in Mick McGahey on mushrooms. Unforgettable.”

Roy Harper plays the Usher Hall, Edinburgh tonight (Saturday, September 17).