You could call it a second chance. In 1935, when George Gershwin gave his first opera, Porgy and Bess, it’s premiere, he did it not in an opera house but in a Broadway theatre. The composer’s reasoning was endearing. “I hoped,” he said afterwards, “to have developed something in American music that would appeal to the many rather than the cultured few.”

Now, Trevor Nunn is taking him at his word. On Wednesday, his production of Porgy and Bess began previews at the Savoy Theatre, its avowed intent to take what is now an opera-house standard equipped with stonking tunes — Summertime, It Ain’t Necessarily So — and through heavy adaptation lend it the mass appeal that Gershwin intended.

The story of an unlikely romance between a cripple and a coke addict in the black slums of Charleston ran for 124 performances at the Alvin Theatre — some achievement for an opera, but, back then, a failure for a show. Its fusion of jazz, gospel and classical traditions upset two very different sections of society: the guardians of culture; and the protectors of black identity. Duke Ellington declared: “No negro could possibly be fooled by Porgy and Bess.” Even today, the libretto’s large-scale use of “dems”, “das” and the “N word” have ensured the piece the same dubious reputation in sensitive liberal circles as Jerome Kern’s equally well-meaning and patronising Showboat.

But it was the concerns of the operatic purists, epitomised by a notice of outrageous snobbery from the composer-critic Virgil Thomson, that really got to Gershwin. That review declared that Thomson and other composers could “never compete with Gershwin for distribution, nor he with us for intellectual prestige”. After the notices Gershwin was said to have been depressed for the first time in his life.

No doubt then that the writer of Swanee and ’S Wonderful saw Porgy and Bess as several steps above the musical comedies that comprised his previous dramatic output. For the rest of his short life, he would declare the opera to be his greatest work.

All this suggests that “musicalising” Porgy might have offended Gershwin. Gareth Valentine, the man charged with adapting the score in Nunn’s version, disagrees. “I don’t think he would have disapproved,” he says. “Gershwin wasn’t like Arthur Sullivan. He never came to hate his popular musicals. They made him rich, and he wasn’t a musical snob.”

So how does Porgy need reworking? “In a musical, words and story come first. We’ve taken out the recitative and changed the keys to take the voices into more elocutionary registers — you can hear the words.” The recitatives have been replaced with dialogue and themes repeated and reworked as dance numbers.

Gershwin did not mind changes: in the Alvin Theatre production, he was not so precious that he was unwilling to make cuts to please his worried producers. In the year before he died, of a brain tumour at the age of 39, he tried to persuade Hollywood producers to make a movie version. Spurned by both the elite and the public, he still hoped that his work would one day please both.

Porgy and Bess, Savoy Theatre, London WC2 (www.theambassadors.com/savoy 0870 1648787), opens on Thursday