HE has two new plays at this year's Edinburgh Festival Fringe, but Irvine Welsh is already thinking about another important third instalment.

Welsh, whose two productions, Performers at the Assembly Rooms, and Creatives, at the Pleasance, open for previews today, is planning to write about what happens next to the characters of Trainpotting and Porno: Renton, Sick Boy, and Begbie.

The writer said that he does not know if their new adventures will be made into a third movie - he says that decision is up to film maker Danny Boyle and his collaborators - but he is already seeing where Renton's adventures lead next.

As the first shows of Performers and Creatives are on at the same time at the Fringe today, the writer said, he would not be attending either, and will see his beloved Hibs play Partick Thistle instead at Easter Road.

Performers, a collaboration with Dean Canavagh, is a black comedy set around the 1960s film Performance, while Creatives is a "darkly comic pop opera" written by Don de Grazia.

However, although the writer said he wants to write more theatre, he is also thinking about the next chapter for his famous Trainspotting characters, first introduced to the world in his seminal 1993 book, and followed up by Porno, the basis for the Trainspotting 2 movie of last year, in 2002.

Skagboys, a prequel, was published in 2012.

The writer said: "I can't look at Trainspotting 3 as a film, that is for other people to do that.

"That is Danny [Boyle] and John [Hodge] and Andrew [Macdonald], the two Ewans [Ewen Bremner and Ewan McGregor] and Bobby [Carlyle] and Jonny [Lee Miller]: we are all in this together.

"All I can do is set the ball rolling by bringing out the source material, and that's what I have been looking to do.

"Just to get another: maybe it will be one of the last Trainspotting-themed books.

"I just got into it, thinking of where they might be.

"I have to take responsibility for the literary world of it, and that is about as much as I can really do."

Welsh is not appearing at the Edinburgh International Book Festival this year and said it is an unusual year, with two productions at the Fringe, which officially opens this weekend.

"Nothing at the book festival this year, but plenty at the theatre side of the Fringe this year, which is interesting," he said.

"We've been in rehearsals a lot and I will catch up with them over the weekend.

"The two press days are [Saturday] but I've decided because they are at the same time, I am not mad about going to see one and not the other, so I am going to see Hibs instead."

Of writing for the theatre, Welsh added: "I think I will write more theatre, but the thing that is frustrating about it, is that it is very much a critic's medium, because it is very much in one place, one land-locked spot.

"You can have great box office and the audience go wild about it, but if the critics don't like it, you are pretty much f***ed, and it's a lot of work and then you are shut down by half a dozen people.

"I think also you have the opportunity to work with actors, which is always a pleasure, because they are story tellers, and they come up with more stories than writers."

This year's Fringe programme, its biggest to date, covers theatre, dance, circus, comedy, music, cabaret, exhibitions and spoken word events.

Famous names at the Fringe include Ruby Wax, Sue Perkins, Sean Hughes and Dead Ringers star Jan Ravens.

Craig Ferguson, who last performed at the Fringe 24 years ago before leaving Scotland to find fame in the US, returns to the capital.

Other notable events include Hibernian Football Club becoming a venue for the first time.

More unusual locations for Fringe shows this year include a boat and a hotel swimming pool.