There was no particular plan for Paul’s sixteenth studio album: just a batch of songs that needed to be put down, and the idea of doing it with a young producer, with someone who could bring something different. Of course, any producer, young or old, would jump at the chance to work with the world’s greatest living songwriter, so the initial intention was to go in and work with a handful of big-but-youthful names, and see which turned out the best. There was Paul Epworth, co-writer and architect of Adele’s monstrously successful 21, and innumerable cool indie records. And there was Mark Ronson, the man perhaps most notable for making Amy Winehouse’s classic recordings but, even putting that to one side, also with a jaw-droppingly impressive collection of credits. Plus the fact that, as Paul puts it, “he DJed at mine and Nancy’s wedding, and kept us dancing till 3am. So I knew I liked his taste.”

Also, with strong links to Paul’s past but also focused firmly on the future, there were Giles Martin and Ethan Johns. Their fathers are both known for their roles in music that no-one will ever forget – “I did a lot of work with Giles’s Dad, George, in Beatles days; Glyn Johns worked with us on Let It Be and Wings stuff” Paul says, just in case anyone needed reminding – but their sons are two men with their own reputations for excellence. Ethan made the Kings Of Leon’s much loved, grittier early albums and, more recently, both Vaccines records. Giles had the advantage of having worked with Paul on “things like Love, the Beatles’ Cirque du Soleil show, also the Olympics opening ceremony and then on some music I did for a new video game called ‘Destiny’ which comes out next year.”

“All the hot producers seem to be the age of the sons of my contemporaries,” McCartney notes. “But with those two, like their dads, they’re great guys who are serious about they do; they had a lot to live up to - but they all proved themselves.”

So four extremely strong contenders, from whom there could only be one winner. Except that… Paul explains, “It turned out I got on with all of them! We made something really different with each producer, so I couldn’t choose and ended up working with all four. I ended up falling for them all. We just had a good time in different ways. Ethan was a bit more acoustic-leaning, Mark would be a little more R&B… they each had a different approach but were all great in their own field.”

And so the idea for New became that it would be a multi-producer Paul McCartney album: with four distinct styles, four different sets of ideas, coming together into one. “It's funny, when I play people the album, they’re surprised it’s me,” says Paul. “A lot of the tracks are quite varied and not necessarily in a style you'd recognise as mine. But I didn't want it to all sound the same. We had a lot of fun.”

First up for a dose of fun was Paul Epworth, who did what anyone presented with 20 new Paul McCartney songs to record would do, and decided put them to one side and jam something more. “I feel like I thrive as a producer from getting in a room with somebody, and making music from scratch,” says Epworth. “He came down for a meeting, to sit down and have a chat, and within an hour we were in the live room with him on bass and me on drums – that was definitely a pinch yourself moment! – and within 20 minutes we had this riff together, which became the first song on the record.”

“It’s hard not to get caught up in that kind of excitement,” enthuses McCartney of the experience, which took place in Epworth’s small London studio. “It's similar to my Fireman project and I like working like that. It’s always a motivating thing for me, having to clear the backlog before I can write more, to realise you suddenly have enough for an album. But Paul had an idea for us to write something new. So even though I had 20 songs, the first one we put down, the opening track, we wrote in the studio just off the back of Paul's enthusiasm.”

That song, "Save Us," with the kind of modern-yet-retro, frenetic and fuzzy guitars that so characterised The Strokes, certainly lives up to McCartney’s claims of not being in a style that you would associate with him. And Epworth’s contribution to the record is more than evident on his other two tracks, which took shape in Paul’s Hog Hill Mill studios in Sussex: "Queenie Eye" has more twists and turns than you would have thought possible to cram in to a mere 3 minutes and forty seconds, while "Road" – which closes the album – subtly builds from lounge-y rimshots-and-xylophone groove into something approaching an epic.

“I felt like it was important to keep doing stuff to these songs, try to look for things in them that were… not referencing things Paul had done in the past, but of a similar spirit,” says Epworth. “So you go from the slightly esoteric, meandering of ‘Road’, which is almost a psychedelic blues thing, to ‘Queenie Eye’, which is quite a tough rock’n’roll song. Paul creatively is very open minded: he’s able to create something and then step back and take a judgement on whether he likes it or not.”

Next came the first Mark Ronson contribution to the album – the title track – also the most straightforward of the set, and the most familiar sounding, with jaunty echoes of "With A Little Help From My Friends" or "Penny Lanel" and the sort of effortlessly beautiful, airy yet sophisticated melody that made Paul McCartney who he is today. “It’s a happy, positive, summer love song,” says Paul. “It makes me think of driving across America in a Cadillac – so hopefully people will think of the sunshine when they hear it, so when we get into the autumn it will give them a little summer feeling!”

Mark’s other contribution, "Alligator," afforded him the opportunity to get his hands on the original four-track recorder from Abbey Road that Paul had used on a lot of his solo recordings made post-The Beatles, up in Scotland. “That was one where we experimented a lot. Because his music is just so all around us now, we forget that Paul, with The Beatles and solo, was always on the cutting edge of technology. So it makes sense that he would want to try out all these new pieces of equipment. We used a TC Helicon for the vocals, which is what Kanye uses a lot on his stuff, so there’s some really interesting things going on with the vocals in the bridges of that song.”

Ethan Johns’ experience of working on "Early Days" and "Hosanna" reflects a similarly, likeably loose attitude in terms of what was going to happen. “There was no plan,” he remembers. “It was, ‘Let’s just go into the studio for a few days and see what happens. I walked through the door with no preconceptions with what I was going to do. It was a complete blank canvas. I’m not even sure in his mind he has a defined idea of what he wants to do. He wants to react to the moment. It was very much, ‘What do you feel like doing?’”

Paul McCartney concurs: “If you said to me now, ok, this afternoon you are going to sit down and write a song, that would really excite me - I just love delving into that area and trying to write something – and taking that into the studio is another kind of excitement because then you get to play around with it.”

“He had a CD, which had a number of titles on it,” Ethan continues. “But then he said, ‘I’ve got this song called ‘Hosanna’, and played it through on acoustic guitar. And the feeling of it was… I mean, I just lit up like the sun when I heard it, because I could feel the inspiration, the connection, the musicality of it. It wasn’t trying to be something it wasn’t, it just was. It was right. So it was simple. What you hear on the record, that’s pretty much it. Just him playing, with a couple of mics set up.”

From the most stripped down moment on the album we come to – last but very much not least – the contribution of Giles Martin who weighed in with five tracks (six if you count the hidden track "Scared"). Perhaps continuing on from the unique experience of re-arranging pieces of The Beatles back catalog into something new with the Love album, he brings perhaps the most sonically adventurous sections of the record. "On My Way To Work" sees simple acoustic guitar/processed drum beat beginnings mutate into huge psychedelic swoops of noise. There’s "Looking At Her," which starts out as a classic McCartney melody, then responds to the line “Me, I’m just losing my mind” with huge, explosive blasts of Moog noise. 'Appreciate" has a lo-fi, almost hip hop feel, with a strange effect on the vocals, layers of heavy fuzz-organ and treated guitars.

“With things like ‘Appreciate’, we had all these tape loop sounds that he’d brought in, and guitar loop sounds,” says Giles. “And we started chopping it all together into this big collage, and I remember saying to him at one point, ‘We should try and make this into a song’, and he just gave me this look, like, ‘You’re so boring!’. Then we found this chorus that he’d done previously, over something completely different, and we spliced that together and it all just worked. That’s one of my favourite tracks on the album, I listen to it in a lot of different ways.”

That said, for all the experimentation and adventure contained within these tracks, it’s clear that Giles Martin is also a producer who knows when to step back and let things breathe. "Everybody Out There" is a straight up, driving Macca pop song that arrived almost fully formed, while "I Can Bet" has a pretty distinct Wings vibe. And then, best of all, there is that hidden track "Scared": just one man and a piano with lines like “I’m scared to say I love you” exhibiting a fragility, a nakedness that we’ve not heard from McCartney in years. “We tried various things, various arrangements,” says Giles. “But to me this had to be just him on his own. Funnily enough, I was talking to Ethan about a thing his dad had said to him, which was ‘When the hairs on the back of your neck stand up, you should just step back’. And ‘Scared’ is one of those. It’s a great end to the album.”

And so, with what is unquestionably his most intriguing record in years – and possibly his best – now completed and ready for the world to be wowed by, it is obvious to its creator what he must do next. Take a break? No. “The next thing for me is to get together with the band and learn the whole album,” he says. “I'm really looking forward to it – I've never done that ‘Play the entire album’ thing. People have asked me about this before and I’ve always said I've got too much other stuff to play, but now I'm really excited to see how the songs will sound – there are a few I have my eye on that were made to play live!”

So onwards Paul McCartney goes, never resting on his laurels, refusing to simply trade on his none-more-formidable reputation, in search of the new…

1.  Save Us (produced by Paul Epworth)

2.  Alligator (produced by Mark Ronson)

3.  On My Way To Work (produced by Giles Martin)

4.  Queenie Eye (produced by Paul Epworth)

5.  Early Days (produced by Ethan Johns with additional production by Giles Martin)

6.  New (produced by Mark Ronson with additional production by Giles Martin)

7.  Appreciate (produced by Giles Martin)

8.  Everybody Out There (produced by Giles Martin)

9.  Hosanna (produced by Ethan Johns)

10. I Can Bet (produced by Giles Martin)

11. Looking At Her (produced by Giles Martin)

12. Road (produced by Paul Epworth)