They’ve erected statues to the man, and named locations and classy guitar models in his honour. All of that is very gratifying. But for long-term admirers, you can’t beat those moments when you drop the stylus – virtual or actual – turn up the volume, and listen in awe to the latest product of Rory Gallagher’s extraordinary, audacious talent.

There will be much dropping of jaws in the coming weeks with the arrival of Blues, featuring 36 mostly unreleased recordings, some acoustic, some electric – and almost every single one of them truly electrifying. No songs are duplicated. Some are culled from studio sessions for various albums – from Deuce in 1971 right up to Jinx in 1982 – while others are from stage shows and lost radio station sessions. There’s also a small number from recordings with artists of the calibre of Muddy Waters, Jack Bruce, Albert King and Lonnie Donegan.

The entire project was piloted by Daniel Gallagher, nephew of Rory and son of Donal Gallagher – the latter having kept the Gallagher flame lit for several decades since Rory’s untimely passing in 1995. It was Daniel’s role to listen to all available tapes, follow up rumours about numerous others, decide which tracks best fitted the Blues theme, sort out the best takes, fit them all into a working running order and look after the editing and the packaging. As somebody once said, “simples!”

“The project was a long time in the works,” Daniel recalls, “but the great thing was that there was so much to choose from. Of course, some of the tape boxes had scant information on them, but it was also often hard to choose the best version of a particular song. For example, initially there were five really fine recordings of ‘Can’t Be Satisfied’ and I had struggled to pick one. But then just as the project was near completion, I heard that a German guy had a version of it that I hadn’t known existed. It had been recorded for Radio FFN in Lower Saxony in 1992, and features Rory’s National slide guitar. When something that great lands in your lap, even at the last minute, it picks itself.”

In fact radio station sessions were a rich source for tracks. Apart from RTÉ providing dynamic performances of ‘Secret Agent’, ‘Want Ad Blues’ and ‘Walkin’ Blues’, the BBC was the location for a sparkling version of ‘A Millions Miles Away’ from 1973, as well as ‘Off The Handle’ from The Paul Jones Show in 1986. But WNCR in Cleveland had gems to offer too, especially a gritty version of ‘Bullfrog Blues’. Daniel says that much of the Cleveland material was recorded because of Rory’s almost insatiable love of playing.

“What happened was that Rory was due to play a concert in Cleveland in 1972,” he reflects. “But it was cancelled because the venue was flooded. So he dropped into the local radio station and played for the DJ instead. Then, at the end of the tour, he came back to the station and recorded enough for what might become a future 2-CD set, if we can clear all the necessary permissions.”

Some of Daniel’s own personal favourites include ‘As The Crow Flies’ from the 1973 sessions for Tattoo, and ‘What In The World’ and ‘Nothing But The Devil’, glorious live versions from the Glasgow Apollo in 1972.

“I also came across a take of ‘Prison Blues’ that had been recorded during the Blueprint sessions in 1973,” he explains. “None of us knew this existed, and it has Rory on acoustic guitar with his voice in great shape. After a while, he’s joined by an unnamed pianist. It wasn’t included on the Blueprint album when it was released, so I spoke to Gerry McAvoy and he couldn’t even remember the song being recorded at all. It seems that it was done impromptu in the studio, probably during a break. “Finding such terrific tracks made the project so exciting to work on, as I never knew what we might unearth next. In fact, in trawling through Donal’s great collection of archive material, I came across the telegram from 1975, in which Albert King invites Rory to play as his guest on a live concert. We were able to include ‘You Upset Me’ – an unreleased track – from that show.”

There was one disappointment that Daniel had to suffer: those who recall the stories about Rory joining the Rolling Stones might get an extra kick out of this one.

“In 1973 Rory was invited to London to record something for a Jerry Lee Lewis tribute album,” says Daniel. “At one point, Rory suggested they do the Stones’ ‘Satisfaction’. Jerry Lee didn’t seem to know the song, although Rory also wondered if he was just pretending, Jerry Lee being Jerry Lee. Anyway, Rory went into the vocal booth and laid down a guide vocal for him. It must be the only time Rory sang a Stones song. Sadly, although it’s a fascinating bit of history, we couldn’t get permission to use it.”

Apart from cleaning up some of the older tapes from the Glasgow Apollo live shows, Daniel did virtually no editing on any of the tracks, and I suspect he would have regarded any suggestion of overdubbing as an act of vandalism.

“Part of the beauty of these recordings is that they needed nothing extra,” he says. “In a way, it would have been an insult to Rory and his fans to add anything. Besides, it’s all there already, wonderfully raw and exciting and pure Rory.”

Daniel admits there are many reasons for Rory’s growth in stature over the years.

“Thanks to Donal’s efforts, we went from a situation where it was even hard to find Rory on CD at all, to the situation now, where there’s so much wonderful material out there. Rory was such a true artist, who followed his own muse and refused to be distracted, and he continues to mesmerise fans and musicians alike with his playing. That’s why blues legends like Muddy Waters and Albert King were so happy to play with him. They knew he was the real deal. There was nothing fake about Rory.

“Many terrific musicians, including Alex Lifeson from Rush, have openly spoken in praise of Rory, and admitted how much they learned from him. I think his appeal might also have something to do with his broad interest in the blues. He didn’t just stick to one style – like Chicago blues, say – or follow one of the legends like Muddy Waters. He could switch from one to the other, and sometimes blend them together in his own unique way. For example, the version of ‘Secret Agent’ on the Calling Card album is a full-on rocker. But the one we found recorded for the RTÉ programme Me And My Music shows how he turned it into a John Lee Hooker-style work. I think this collection proves how versatile he could be.”

There’s also the added attraction of hearing Rory himself talking about his influences, and how his love of the blues grew, on a short recording that appropriately concludes the set. And he never had any interest in the showbiz side of the music scene.

“Rory just wanted to play the music he loved,” says Daniel. “And talk about the music to his fans. He had no interest in developing an image or picking a suitable hairstyle or worrying about wearing the right jacket. Stardom had no appeal for him at all. He preferred to let the music do the talking, and I think that this Blues set says it all. I only wish Rory were still here to hear it.”

• Blues is a 3-CD 36-track set, out now from Universal Chess. There is also a 16-track single CD, and a double vinyl set.