Henryk Górecki's third symphony is one of the best-selling classical music pieces of all time – although critics initially hated it. His fourth, completed by his son after the composer's death in 2010, will premiere this weekend. Here is its remarkable story • On Monday 14 April, the Guardian will host the exclusive video premiere of Górecki's fourth symphony, performed by the London Philharmonic

It wasn't an auspicious start. When the Polish composer Henryk Górecki's Third Symphony, his "Symphony of Sorrowful Songs", was played for the very first time at a festival in France, it went down terribly. Appallingly, in fact. The senior French musician sitting next to Górecki, probably the composer and conductor Pierre Boulez, the doyen of the international avant-garde, shouted: "Merde!" The critics called it "decadent trash" and "endless". Why? Because Górecki's repetitions of simple melodies and harmonies, and his setting of movingly "sorrowful" texts about motherhood and loss for solo soprano were heard as a sentimental, slushy sellout. Instead of modernist angst and objectivity, Górecki gave his audience heartfelt tunes and instant emotion. Stylistically speaking, his symphony must have sounded like a Cliff Richard number in the middle of a Slayer gig. Not good, in other words.

That was in 1977. But fast-forward 15 years, and the very same piece would become the most successful piece of contemporary classical music of all time – precisely because of its easily appreciated melodiousness, and its slow, sorrowing soulfulness. Thanks in part to the airtime the work's second movement received from Classic FM, the 1992 recording of the 55-minute Third Symphony – with soprano Dawn Upshaw and the London Sinfonietta – sold 700,000 copies globally in a couple of years, and it's now notched up more than a million sales. Eat those stats, Pierre and the avant-garde!

But here's the paradox. As a creative figure, Górecki, who died in 2010, was much closer to Boulez and the avant-garde than the Third Symphony might make it seem. Górecki wasn't interested in pleasing his audience or pandering to their tastes for commercial gain. As he said in 1994: "I never write for my listeners … I have something to tell them, but the audience must also put a certain effort into it". Surprised by the belated international fame of the piece, Górecki said that "perhaps people find something they need in this piece of music … Somehow I hit the right note, something they were missing. Something, somewhere, had been lost to them. I feel that I instinctively knew what they needed."

Yet for all its totemic success, the Third Symphony failed to catalyse similar interest in the rest of Górecki's music. And anyone who has ventured beyond the lamenting strains of the Third Symphony is in for a shock: try Górecki's Second Symphony, composed just a few years before the Third, which contains music of unrelenting, noisy monumentality. His even earlier music, of the late 1950s and 60s, is more adventurous still, indebted to composers like Karlheinz Stockhausen and Luigi Nono, precisely the kind of modernists his later work would alienate. His choral music, such as his Beatus Vir, contains passages of ritualistic, hieratic power, and his later music, composed in the wake of the Third Symphony, is full of stark, often violent contrasts. As a whole, Górecki's music is the exact opposite of the easy listening and emotional gratification that so many listeners found in the Third Symphony.

The question was, how would Górecki follow the Third when he came to write his Fourth Symphony, three decades later? At his death, the Fourth was completed only in short score – a composer's shorthand rather than a full-fleshed orchestral version. The task of finishing the piece fell to his son, Mikolaj, also a composer. Originally planned to premiere the year of Górecki's death, the Fourth Symphony is finally on the brink of its first performance, from the London Philharmonic Orchestra, on 12 April.

Mikolaj describes the piece as "very different from its immediate predecessor … and is closer to monumental works like Symphony No 2 or Beatus Vir and to later pieces with Tatra folk influences such as the Little Requiem". He remembers the effect the success of the Third Symphony had on his father: "The way he related to this sudden fame influenced his future attitude. To put it simply, he wanted some privacy, and after the success of the Third it was not easy for him to enjoy this."

Working on the Fourth Symphony has been a powerfully emotional experience for Mikolaj: "I have felt my father's presence throughout my work on the symphony. I am privileged and honoured to be involved, but it absolutely does not belong to me".

Mikolaj has had to live his musical life in the shadow cast by his father's life and music in Poland. "For many years I kept it a secret that I was composing. When I was aged 13 in high school, by coincidence, my father found out about it. After learning that I really wanted to write my own music, he was always highly supportive, and we discussed composers. It wasn't easy to disagree with him, but fortunately we only differed a little in our favourites. He was close to Beethoven, me to Mozart. He preferred Strauss, I favoured Mahler."

The posthumous premiere of the Fourth Symphony caps Górecki's reputation as an orchestral composer, but it also contains some surprises. The music, which pays homage to another, older Polish composer, Alexandre Tansman (its subtitle is "Tansman Episodes") features some brutal juxtapositions of massively powerful music with slow, intimate passages for solo instruments, including prominent parts for piano and organ. And towards the very end of the four-movement piece, there's an enigma, something Mikolaj describes as "an intriguing Wagner quotation … the composer was a huge rediscovery for my father in the last years of his life". Having seen the score, I can sense that Górecki's Fourth Symphony contains a bigger range of expression, and is a more ambitious musical achievement than its predecessor. Will it sell a million copies? Well: it all has to start with the first performance …

Reading on mobile? See Górecki's Third Symphony performed here