VAN Morrison’s idea to make an album of duets has been around for years but only now has it all come together.

“It’s what you call a side project,” says the 69-year-old Northern Irishman, whose 35th studio set Duets: Re-Working The Catalogue will be released on Monday.

In the past, Morrison has recorded several duets with John Lee Hooker, a couple with Tom Jones, and others with Ray Charles, Carl Perkins, Bobby Bland, Lonnie Donegan and Georgie Fame.

This time he had “great difficulty” in choosing the guests. He explains: “I had to leave a lot of people out because of the time factor and it was going to run into a double or triple album. I just had to get people who were available. It started back in October 2013. I wanted Bobby Womack – he had been one of the first people on my list for many years.

“So Bobby Womack, Mavis Staples and Natalie Cole were playing the Blues Festival in London and so was I. That made sense to get them during that. Those three kind of kicked it off for me. Then it was much harder to get the rest of it because of calendars.”

Was it important to Morrison to have people recording face-to-face with him in the studio? “Absolutely, yes, yes. You want to get that whenever possible. It is not always possible because of calendars as people are all over the place and very busy. Whenever possible you want to get that,” he says.

“The George Benson track I did live with his band in the studio because I wanted to do something with his band rather than mine for a change. You just have to work with what’s available at the time. Luckily he was in London at the time, his band was there, so it worked out.”

Morrison is a notoriously quick worker in the studio. “I’m from the John Lee Hooker school of, ‘you get in, you get out’, kind of thing,” he says.

Such a working practice was no harder for these duets as long as the artists were available, like George Benson for Higher Than The World. “He was there that day, we did it, it was a great couple of takes and we were out of there having lunch by 3pm,” recalls Morrison.

Rather than re-interpreting Morrison’s best-known numbers, he saw the album as a chance to “rework the catalogue”, when no one else was doing that, hence the album title. “You have publishers but it is lip service really; it is not like the old days where you had a publisher that was going to work your songs. So that was the other strand of it,” he says. “There were two parts to it; one was the fun of doing duets, the other was re-working the songs as no one else is working them. So I have to work them. It’s like working the catalogue.”

He has done just that with the likes of Bobby Womack (Some Peace Of Mind); Mavis Staples (Lord, If I Ever Needed Someone); PJ Proby (Whatever Happened To PJ Proby?); Mark Knopfler (Irish Heartbeat); Canadian crooner Michael Bublé (the single Real Real Gone) and North Yorkshire jazz chanteuse Clare Teal (Carrying A Torch).

Meanwhile, turning his thoughts to wider musical matters, Morrison can no longer relate to “what they call R&B”. “It doesn’t have any rhythm in it. It doesn’t have any blues. To me it is very unrhythmic. Its very robotical I find. I don’t know what that is,” he says.

“The words take on different meanings after a while. It’s like the word ‘spiritual’. What does that mean? It could mean anything now. Like a hundred years ago that meant mediums, séances or something. Then it meant something else later on, then there is a new age version of it. So you don’t know what these words mean anymore; in fact it doesn’t mean very much because it’s over used. So you have to find something else.

“It’s like soul, I don’t know what that is now. To me soul was like Ray Charles, Sam Cooke, Bobby Bland, Solomon Burke, Bobby Womack. But what is it now? It is just a word, it can mean anything.”

Morrison is on a roll now. “What is jazz? Some of the stuff that they say is jazz, I don’t know what it is,” he says. “Blues also. Something started with Jimi Hendrix. So the jumping-off place was really loud guitar and feedback, then that became the blues. To me that’s not blues; blues is like Junior Wells and Buddy Guy in a club live. That was the blues for, you know, John Lee Hooker even up to modern stuff that John was doing; that’s the blues, like The Healer, that’s the kind of thing.”

Does Morrison feel optimistic or pessimistic about the way the blues and jazz traditions are going? “Well, I just feel like you know what you know and you just get on with it. I don’t really know if there is any tradition anymore,” he says. “I was lucky to meet these people, get to know them, hang out with them, learn things, observe stuff.”

Better still he has now worked with plenty of them too.

• Van Morrison’s Duets: Re-Working The Catalogue will be released on RCA Records on Monday.

By Clive Davis and Charles Hutchinson