Here is an accurate measure of age in rock'n'roll years: react to the use of the word "only" in the next sentence.

On his next birthday (the now all-too-memorable September 11) John Martyn would have been only 63.

It is two and half years since one of the most inventive songwriters and musicians that Scotland has produced died of pneumonia after a long spell of serious illness undoubtedly brought on by his hard living in earlier years. But in an age when we are well used to seeing performers playing major stages in their eighth and ninth decades, dying at 60 seems much too young. It is equally true that anyone who saw him in his latter years might have guessed that he was rather older.

There are signs, however, that the legacy of the man born Iain David McGeachy and brought up on the south side of Glasgow is being re-assessed and his undoubted influence properly recognised. Next month a double CD, Johnny Boy Would Love This, is released on Absolute Recordings, featuring 30 cover versions of Martyn’s songs by such diverse talents as Beck, David Gray, Phil Collins, Robert Smith, Morcheeba, Beth Orton and Scotland’s own Paolo Nutini and Snow Patrol.

The tribute disc comes from the same label who put out Martyn’s last recordings, under the title Heaven And Earth, in May. Taken together, they represent a long-overdue lively memorial to the man, who – as Orton observes in the verbal tributes accompanying the August release – invented the whole idea of “folktronic” music, decades before someone invented the term.

One of the men behind both the salvaged last album and the new tribute set is producer Jim Tullio (known as Tools to most in the business) and there is no doubt that the time he has devoted to Martyn’s legacy is a reflection of his deep affection for the man.

“He exuded music like you and I speak,” says Tullio. He illustrates this theory with a story of Martyn insisting on adding his own keyboard track to one of his last songs. The producer indulged him as the guitarist played what sounded to him like “nonsense noodling”. However when it was added to the existing track it fitted perfectly.

Recognition of that talent dictated the sound of the Heaven And Earth disc. “We left it exactly how he last heard it, in terms of its structure. We could have made it more ‘pop’, but John was not a pop artist. So we kept every morsel of him. Some of these songs were off the cuff, but they are great songs.”

It is certainly arguable that the title track, Willing To Work and Could’ve Told You Before I Met You on the disc stand comparison with Martyn’s more famous work, and Stand Amazed is, as Tullio puts it, “a great groove”. “He was one of the great songwriters, but he very rarely wrote a bridge. The songs simply didn’t need them because the verses and choruses were so strong.”

Martyn was, however, by no means a saint, even after his abuse of his own body had led to his losing a leg. His wife Beverley has recently published a memoir that makes it clear quite how far from canonisation he was in his more angelic-looking days. Tullio says there was no doubt about his professionalism however.

“Sure, he was difficult, and everybody knows he drank a lot, but when he came to work he knew his stuff and he meant business. I don’t think it is true to say that he was self-destructive, because he loved life. He had the metabolism of a bull but he was an intelligent guy and he knew the drinking would get him.”

Johnny Boy Would Love This: A Tribute To John Martyn is released on August 15; Heaven And Earth is out now.