Coldplay's new album is ready for release, and paparazzi-hunted Chris Martin emerges from hiding long enough to share his thoughts with Brian Boyd about celebrity, responsibility and ripping off their favourite bands.

The tariff barriers facing Ghanaian farmers or Gwyneth Paltrow? Chris Martin knows which one people want - and which one they're going to get. "I can't believe that people think that by starting off asking loads of questions about Coldplay, that somehow I am then going to start opening up about my private life," he says.

Oh dear. Bang goes the "Great album, Chris, how's Gwyneth keeping?" question.

"What you have to understand is that for the last two years all I've had is photographers following me around all day, and questions and questions about my personal life," he says. "It was either that or people who hated Coldplay, who hated me, or just wanted something from us. That's why this interview is making me really emotional. This is talking to an old friend - you know where we come from. We can talk about Ocean Rain. This makes me want to cry, I'm talking about music again for the first time in two years."

Since the last album, A Rush of Blood to the Head (2002), Coldplay have become the U2-in-waiting. Initially the band were viewed, in a jaundiced manner, as the "new Radiohead" (how empty that sounds now) and attracted the same self-loathing criticism that Keane now attract. You know: Martin is a nice middle-class boy with a first-class degree in Ancient World Studies who doesn't do the whole leather trouser/crack cocaine thang. Martin called Rush of Blood Coldplay's War, but it went on to become their Joshua Tree. Now, with the band touching 20 million album sales, it's sanguinely predicted that their new album, X&Y, will make them the biggest rock band in the world - something which would be greatly expedited if U2 took the trout farm option.

One celebrity marriage later and Martin is now more of a fixture in Heat magazine than the music press.

"I know, and it's made me a lot more fond of music journalists, that's for sure. I'm not bitter about what that type of press has done to me over the last two years, just very, very, very scared. My overwhelming emotion when it comes to the press is one of being absolutely terrified of being brought down - that's what I fear the most. Someone is going to say something or do something that's going to bring me or a member of my family down. The paparazzi are trying to get me into trouble. I feel like everyone is trying to get me into trouble and I object to that. I have become very guarded and suspicious of people.

"It's even stuff like there was this story that because we didn't finish the new album on time, the EMI [Coldplay's record company] share price went down by 16 per cent and it was all our fault. The company wanted this album out in March to fit into some financial quarter they had, but we weren't finished. People were ringing me and saying 'have you seen what is says in the papers about Coldplay and the EMI share price?', and I'm just going: it means nothing to me. Pandering to shareholders has been one of the main problems of the last 20 years in terms of the world going downwards.

"It's crazy. I can't believe that story was deemed to be pressworthy, as I can't believe why my private life is pressworthy. The press say it's not our fault, we're just giving the story colour, but it still is crazy."

When X&Y didn't come in on time to suit some accountant's ledger book (or whatever they use), there was frenzied talk about "the difficult third album". The only difficulty, it transpired, was a Kraftwerk sample.

"What really happened is that we have a song on the album called Talk, which samples the riff from Kraftwerk's Computer Love. It sounded great, but then someone suggested that it should be our comeback single and we just freaked and scrapped the whole song. Then it wasn't going to be on the album at all, then we did a different mix and put it back on, but it's not going to be the first single. There's a version out there on the internet but it's the wrong version."

The kick-off single is now Speed of Sound, already the most downloaded song ever on the iTunes web shop.

Martin says the album is called X&Y because "calling it Ying and Yang would have been too wanky - it reflects the extreme nature of my day-to-day life". It's an epic, widescreen affair that's destined for a stadium near you.

It's always been a curious aspect of the band's music that, while their songs are mainly made up of minor chords, they still get the tunes to soar. "The minor chords thing is funny," he says. "We stole that from Tears for Fears. Here's how we got the album: my wife was working and myself and Danny McNamara from Embrace were hanging around on the set. Danny had a guitar and started playing Mad World and this was before the Gary Jules version. I was sitting there listening to it and thinking, 'I have got to steal from that'.

"At least one song came out of that. There was that and also just after Rush of Blood came out I found a Post-It note I had written to myself. On it was written 'Try and write a gospel rock record'. I'm always writing Post-It notes to myself."

Your reporter presents Martin with the thesis that Coldplay are the poppier, more successful musical cousin to Elbow. Both bands do minor keys, earnest/mournful lyrics but chase the "Big Music" sound.

"Now that's interesting you mention Elbow. Their Cast of Thousands is one of the very few albums in the last five years that I have played over and over again. I love them, they're just not properly acknowledged. I don't mind telling you that our song on the album, Fix You, came directly from Elbow's Grace Under Pressure. In fact, this whole album for us is an excercise in plagiarism. We really did steal off Elbow for that song."

Martin reaches over the hotel room table for a copy of X&Y. "I'll go through all the songs for you and tell you where we got them from. Square One, which is going to be our opening song at Marlay Park in June and on the whole tour, is us trying to steal off Brian Eno. What If is us trying to rip off John Lennon. White Shadows is ripping off The Cure and U2. Speed of Sound is a Kate Bush song. A Message is from an old hymn. Swallowed in the Sea is a direct attempt to write Fairytale of New York."

Really, it sounds more like The Proclaimers' 500 Miles meets Roger Whittaker to me. "That's mad!" he says. "We wanted that song to be something you could play in a seaport and also, and you couldn't have known this, it was originally written to be whistled!"

"The way we see it is that Fix You anchors side one of the record and Swallowed in the Sea anchors side two. And I really don't mind admitting where they came from. If someone is cross with us for that, then it should really make them champion the original even more, and people might get more interested in the original.

"Having said all that, we really approached this album thinking: 'This is going to be our last album.' Every available bit of energy went into this. We've no more ideas, we put them all into this, we gave it everything - really as if was our last ever album."

Somewhere in Chris Martin's head, given all the "Coldplay singer and his famous actress wife pictured leaving a restaurant" nonsense he has put up with for the last few years, there was an idea just to hand in the master tapes of the album to EMI and then run away from the promo-go-round.

"I really wanted to just release it quietly, not to shove it in people's faces," he says. "After everything, I just wanted it to be about the music and nothing else in my life. And we really were going to do this. Then I went with Oxfam to Ghana and I met the farmers there and learnt about the import of rice and the tariff barriers and the debts and I realised that's fuckin' why I want to do all this. That gave me that last push of energy. I want to make us massive rock stars so we can talk about this stuff, about fair trade.

"It's a selfish thing on my part - this stuff is going to affect my life. I'd be a fuckin' idiot not to talk about it. It's going to haunt all of us unless we do something about it. If we drain 80 per cent of the world, it's going to haunt the other 20 per cent. That gave me the final push. Now we want to tour, now we want to talk.

"This is what drives me. We've won awards, we've sold lots of records and we're still ambitious in that regard. But that's not the biggest reward or, indeed, even the biggest motivation anymore. There has to be more talk about the Make Trade Fair campaign. I'm glad that finally there seems to be an awareness of the root causes of misery, rather than, as we have seen in the past, last minute solutions. I really believe that this War on Terror would not be raging so badly if we hadn't fucked over so many countries trade-wise."

The link between the depredations of African farmers and the antics of the tabloid paparazzi is a bit of a stretch, but Martin gets there. "To go back to the fame thing. This physical thing of having a man follow you around all day trying to take your photograph - it's eerie. There is a pure physical response: if you go up and kick a dog it will bite you. But with them [the photographers] you can't do anything. They are cunts.

"But for all this stupid fame thing, at least whenever they do pap me I'll have the Make Trade Fair sign on my hand - to balance it out." The X and the Y of it.

X&Y is released on June 3rd. Coldplay play Marlay Park, Dublin on June 22nd