Pop stars were never supposed to be 58-year-olds, were they? "At this age of mine, you've just got to make a decision about whether you are going to write for yourself or for the radio," according to Sir Elton John. "I mean, how many ****ing hits can you have?"

The question is rhetorical, an attempt philosophically to brush off the notion that he should care about such things as chart positions and radio play any more. After all, these days he is a titled member of the rock aristocracy, with a hugely successful sideline in musical films and theatre, and a residency in Las Vegas.

The giveaway, though, is the expletive in the middle of the sentence. After a lifetime immersed in popular music, I don't think Elton is ready to be consigned to the veterans circuit just yet.

Earlier this year, it certainly looked as if he was going the same way as Cliff Richard and Status Quo, banished from Radio 1, absent from the charts and increasingly reliant on back catalogue and live performance to sustain a career.

Despite glowing reviews comparing it to his best work, Elton's 2004 album Peachtree Road failed to trouble the upper reaches of the charts. "It is probably one of my lowest-selling albums of all time," he says. "It was disappointing everywhere in the world, so I have to hold my hands up and accept that the songs just didn't connect.

"I'm proud of Peachtree, but, if I think about it logically, people may have 10 or 12 Elton John albums in their collection already. Do they need another one?"

Recent developments suggest the public's appetite for Elton remains strong. Coming off the back of a sold-out stadium tour and an attention-grabbing performance at Live8, he reached number one and number four with consecutive singles.

"When something like this starts to explode, it does put the fun back in it," says Elton, who takes no credit for the single that put him back at the top. Eminem (with whom Elton shares a mutually respectful relationship, despite the rapper's penchant for homophobic insults) remixed Tupac Shakur's Ghetto Gospel, adding a chorus from an obscure 1971 Elton John track, Indian Sunset.

"It was a piece of luck, but, when you have been around as long as I have, things just have a way of happening. It is incredible what Eminem's actually done, combining melody and great hip hop in an original way. It is not a lazy piece of work."

Elton's record company, Mercury, cannily followed that with Electricity, the singer-songwriter's original version of a showstopper from his latest West End musical, Billy Elliot, which went in at number four.

"That's a demo," Elton reveals. "It was never even supposed to be released. When I am working on musicals, I write songs and we record them and mix them the next day then move on to the next one, so we have an idea of what the shape of the show is going to be. I have albums full of songs from Billy Elliot, The Lion King, The Road to El Dorado, just lying around."

The demo was released as a download single tied into a mobile text message competition offering the chance to watch Elton perform in Las Vegas, leading to an enormous response from his fan base. Such was the controversy in the music industry, there are now moves to change the chart rules.

Of course, Elton isn't complaining. Discounting duets and reissues, this is his highest-charting solo single since 1990. "I think it's hilarious. I don't know about all the technical stuff. I am a Luddite. I don't even own a mobile. I just write and record and that's about it."

Actually, he writes and records rather a lot. When he rose to fame in the early '70s, he was in the habit of putting out two albums a year. Recently, preparing Peachtree Road, Billy Elliot and a new theatrical musical, Lestat, based on Anne Rice's Vampire Chronicles (with longtime lyric writing partner Bernie Taupin), he composed more than 60 songs in one year.

"It was one of the most productive periods of my life. Lestat exhausted me. Once I started, it was like being bitten by a ****ing vampire. I couldn't stop. I was sucked dry, but I honestly think that is some of the best work we've ever done.

"The songs are very complex. It's orchestral work, no electronic music at all. It's music from the 18th century basically, written by a 21st-century Luddite."

The show will open in San Francisco in December and move to Broadway in March. Having been a solo star all his life, Elton also enjoys being part of a team. "Doing a musical you've got a director, choreographer, lighting guy, costume person, set creator, conductor. You're all in there together, and so you've got to leave your ego at the door. Some songs won't fit no matter how much you love them. You can't stand there and stamp your feet and say, 'I want that song in!' "

Elton raves about Billy Elliot, which he developed with original screenwriter Lee Hall and director Stephen Daldry. A gripping piece of political and emotional theatre, it has been widely hailed as the most powerful musical of recent years.

"Every time I go and see it, I can't believe I am actually involved in it!" he laughs. Then, as an indiscreet aside, he adds: "Just between you, me and the gatepost, I'm not really a lover of musicals!"

These are the type of remarks that tend to get Elton into trouble. There was a recent spat with George Michael, when Elton said he was "wasting his talent" and suggested a "deep-rooted unhappiness" was to blame. Michael responded with a catty open letter to Heat magazine, branding Elton a gossip monger.

"George and I are fine," reports Elton. "We've had dinner, and I've apologised to him if I hurt his feelings. It was handbags at 50 paces. We like each other too much to fall out."

His spat with Madonna is proving less short-lived, after Elton mocked her live show at the Q awards, saying anyone who mimes onstage should be shot. "That one's slightly more difficult," Elton laughs, guiltily. "I did send her two Christmas cards and they both came back. It was just one of those off-the-cuff things.

"I haven't got Tourette's syndrome but I can't censor myself. Why should I? But let's leave it at that, I don't want it to go any further, for Christ's sake!"

I suspect the truth is that Elton loves all of this, the hurly-burly of the pop world. He still tries to buy every new release, ticking his purchases off in a handwritten bumper folder. He enthuses about new music with the excitement of a genuine fan, eager to share his discoveries (digital soul singer James Lidell and Irish band Hal are current faves).

"When I like someone, I let them know. I drop them a note, call up their record company, whatever. It's not about wanting to jump on anyone else's bandwagon, it's about reaching out."

His latest protégé is James Blunt, who is managed by Elton's company 21st Artists. "He knocked me off the number-one spot, but I am more excited about him than I am about me. It's gratifying to see somebody come through by just playing gigs and being nurtured and not by money and hype. It's like a throwback: it reminds me of what happened to me in America in 1970."

Another of today's rising stars who has attracted Elton's attention is the troubled former Libertine Pete Doherty, who performed a shambolic duet of T Rex's Children of the Revolution with Elton at Live8. "I thought, here comes mainstream Elton, what can we do to shake things up a bit? I think Pete's immensely talented. He came down to Watford and we rehearsed it and it was absolutely tip-top, perfect.

"I have to be very discreet what I say, but I just think he was really nervous on the day. He's a mess, it's really sad. He's so young I don't think that he's going to listen to anybody. But I don't think the people around him set a good example, which is a shame. But, you know, he had his chance to do it and he came on… at least he looked great!"

As you can see, Elton's discretion never seems to last very long. When I ask him what he made of Live8, he groans. "Oh God, here I go. I thought it was a bit of an anti-climax, to be honest. The thought behind it was fantastic, but Hyde Park is a charisma-free zone. There was no sense of occasion and from a musical point, I didn't think there were too many highlights. I was very pleased to be a part of it, but I didn't think it was anywhere near as good as the first one. How could it be?"

He checks himself again and tuts. "People are going to think I am a grumpy old sod, aren't they?"