HE is best known for writing about the dark underbelly of life on the streets of the Scottish capital.

But now Irvine Welsh is to step into new territory and write a musical to be performed this summer.

Welsh will unveil his "popra", set in modern America and the music business, at the Edinburgh Festival Fringe where he already has a play, Performers, scheduled for the Assembly Rooms.

His work, Creatives, has been developed in Chicago, US, where he now lives.

It will feature an eclectic array of music, from rock and roll to hip hop, encompassing funk and country and R'n'B with original music as well as pop classics.

While Performers, which Welsh has written with Dean Cavanagh, is inspired by the making of Scottish film maker Donald Cammell's seminal movie Performance - and the "real villains" enlisted into its production - Creatives is an original and more modern tale.

Welsh said Creatives is infused with music of all kinds and will be staged at The Pleasance venue.

He said: "It's very different, it's not about London in the 60s, it's about Chicago now, and it has been written with my friend [academic and writer] Don De Grazia.

"We are taking it over to Scotland and it will be fun too, it's very different stuff, and it has original tunes by Lawrence Wythe.

"It's very much about America now."

Welsh said it is "very much" a political piece, set in the music business, and is about the "cultural co-operation of music", and will involve "every" kind of music, a mixture of rock and roll, funk, country, commercial music, hip-hop and rap.

He added: "We had it in a workshop situation in Chicago where people could come in and watch it being performed and devised, and it is now very tight and we will bring it over here and see where it goes over here."

De Grazia has described the show as "a pop opera or a popra", and has been initially staged at the Chicago Theatre Workshop, an "incubator for new works".t

On the current situation in American, under President Trump, Welsh said: "If you're a writer its fabulous.

"But it's not such a great time if you are citizen, it's a very worrying time for people.

"But I think it would be worrying anyway, we are at this strange juncture in human history, we are at the end of capitalism now, and the end of paid work, the end of socialism, we are de-industrialising.

"The problem with putting trust in loud-mouthed demagogues is that they don't really know a thing - we really trust our own ignorance, because it is not a time for false certainties."

He added: "Trump is just entertainment basically, for people in America, for people being bombed by him, it's less so."

On the political situation in Scotland, he said: "Again, we are at a strange place, a strange point and its difficult to think of it in isolation.

"One thing I am convinced of, we really need to start breaking up these big imperialistic states, they are not going to do us any good.

"They have become more irrelevant to people - people switch on their TV, particularly young people, and look at all this and think 'this has nothing to do with us at all'.

"The worrying thing about it, we are developing a two tier society....with a world of the power elites and the rest of us just getting on with it, and that separation is just getting bigger and bigger every day."

Performers is a one act play and does not feature fictional versions of Mick Jagger, James Fox or Anita Pallenberg, who starred in Performance in 1968, or "anyone real", the writer said.

Welsh added: "We see as an extended metaphor for all sorts of different things, the sexual revolution of the 60s, it was also the East meets West - the east end of London meets the west end, those kind of differences were breaking down.

"It was a landmark in British cinema, it helped stake out that territory, it wasn't European art house, it wasn't Hollywood, it was a peculiarly dark, British film.

"Its an astonishing film, but the story behind it became more and more compelling, and we wanted to tell the story of two guys, 'duckers and divers', who came along and how it affected them."

The play is being directed by Nick Moran and will run daily at The Assembly Rooms Ballroom from August 3-27.

Welsh said he had received an offer from a London venue already and said "I hope it does well, and I'd love to see it in the West End."