Gary Barlow, a man who has more reason than most to be wary of success's fickle nature, talks about when, not if, Progress will be massive. Two days after the press conference, tickets for the tour are released and four different ticketing websites immediately crash under the demand, which is greater, one agency reports, than for the Michael Jackson London gigs.

This is not, it's worth noting, a state of affairs that anyone could have predicted six years ago, when the ex-members of Take That agreed to be interviewed for a no-holds-barred ITV documentary called For The Record. You get the impression the four band members whom Williams left behind in 1995 said yes to the documentary's director only because they felt they had nothing left to lose: their fortunes had waned almost as dramatically as Williams's star had risen – and it had risen to a degree of success so immense that, as he ruefully notes today, his 2006 album Rudebox can be widely decried as a career-stalling flop despite reaching number one in 14 countries. Within three years of Take That's split, Gary Barlow found himself without a record deal, unable to convince promoters to book him even on a small tour, a state of affairs that left him so distraught he effectively fled the country, relocating to LA. Mark Owen, too, had lost his record deal. There was something of a hike in his profile when he won Celebrity Big Brother in 2002, but not enough to kick-start his musical career: he ended up "spending my last penny" funding a solo tour of Britain's toilet venues. Suicidally depressed by Take That's split, Howard Donald's solo career never even left the launch pad – his debut single Speak Without Words was never released – while Jason Orange's attempts to reinvent himself as an actor were equally short-lived. After a couple of TV and theatre roles, he gave up, apparently unable to stand the audition process, and eventually went to South Trafford College to study biology and history. "Unfortunately, all four of us, especially Gary, of course, were being compared for 10 years with Rob's success, and actually I was really happy most of the time," Orange says. "What did my head in, what really vexed me in the 10 years I had off, if I was on a beach somewhere in Thailand, or at college – things I loved doing and chose to do – it was always going to be considered by other people as, 'Oh, he's taken a step down', 'Oh he's a failure', while Robbie's up there, 'Look at what he's doing now.'" It didn't help that Williams was so spectacularly ungracious in his victory, never missing an opportunity to attack Take That, and Barlow in particular, in interviews or on stage or even in the lyrics of his hit single No Regrets. "I sniped at Gaz," he nods today. "He never sniped at me."

And yet, despite strongly suggesting Take That's 90s heyday had been a cavalcade of squabbling, misery, intra-band wanking competitions and improbable bunk-ups with Lulu, the For The Record film led to their reformation. "When we went into it, no one was really interested in giving us creative control," Barlow says. "We'd given everything away doing that, but we were told it was going to be a good film, and it was." Six million people watched it. A "one-off" reformation tour turned into an extraordinary critical and commercial rehabilitation. It shouldn't have worked, but it did: reconstituted 90s boybands are meant to do a few nostalgic gigs for the benefit of the bank balance and the mums who were once screaming teens, not become bigger than in their heyday. Even the band seem a little baffled as to what happened. They bandy about words like "nostalgia" and "redemption" when asked about their ongoing success, before giving up. "What do you think?" Owen asks, plaintively. "And how do you think it's going to end?"

I first meet Take That in a Park Lane hotel corridor. It has to be said, they look fantastic: rather irritatingly, considering the scream-inducing, fresh-faced pulchritude they enjoyed in their 20s, they seem to be wearing middle age exceptionally well. You might expect that from Barlow, who seemed a bit middle-aged even at the height of Take That's teenybop stardom – listening to him earnestly discuss the varying qualities of different kinds of microphones while Williams groans about fetching his anorak, you rather get the feeling he enjoys playing up to his grey image – but the rest of them look remarkably good in their early 40s, too. Recently married to US TV actor Ayda Field, Williams looks substantially better than the last time I met him, which is just as well, because back in 2005 he looked deeply troubled and gave every impression of being nuts: having invited a group of journalists to hear his then-new album Intensive Care, he proceeded to pick a fight with every single one of them.

Today, he's as friendly and charming as his bandmates, all of them en route to the Q Awards, where they're due to get something called the hall of fame award. It's their first public appearance since Williams rejoined, but they avoid the red carpet, arrive after the other guests, via the back entrance, and leave as soon as they've been handed their gong. This seems to have less to do with avoiding a repeat of the 2006 awards – where the reformed Take That won something called the Q Idol Award, but Arctic Monkeys' Alex Turner rather spoilt the atmosphere of backslapping bonhomie by calling them "bollocks" – than with a determination not to court the celebrity press. "We don't do premieres or quizshows, we don't do the opening of an envelope," Barlow says.

"I don't go out at all now," Williams nods. "The only time people get a photograph of me is at an airport or coming out of the dentist."

"And you are a has-been," Owen smiles.

"I am," he agrees. "A tiny, tiny bit of a has-been."

And so we weave through hotel boiler rooms and service lifts, Williams offering the occasional cheery greeting to the maids and maintenance men who look on in disbelief: "All right, bud?" The atmosphere of mild unreality is heightened by the fact that Orange is carrying a flask that, it transpires, contains homemade chicken soup. "It's delicious and nutritious," he frowns when I ask him about it, as if turning up to a music industry awards do with a flask of soup is the most normal thing in the world. He starts saying something about the food at awards ceremonies, then stops himself. "I'd let you have some," he smiles apologetically, "but there's not really enough."

It's another reminder that Take That hail from an era before the music industry decided it was a good idea surgically to deprive pop stars of their personalities via media training. Today, the five are interesting, engaged and self-deprecatingly funny. They always laughed a lot in each other's company, Orange says, but in the 90s, "it was a laugh that didn't go all the way to your belly, not ungenuine, but a little bit hollow, there was always that thing of, we've been put together, we're not mates." They are also rather more thoughtful than their public image suggests. At one juncture in the interview, Orange will ruminate on the subject of male angst ("There's a lot of talk at the moment in a lot of magazines and newspapers about men being in crisis, isn't there?"). With the best will in the world, this is not a topic anyone would have expected to hear much about from Take That when Why Can't I Wake Up With You? and Babe were bestriding the charts.

Rather pleasingly, they also seem unconcerned with hiding their differences – evidence, presumably, of a frankness within the reformed band by which Williams seems to have been a little taken aback. "When there's a band meeting, they can't half say some earth-shattering stuff to each other," he says. "The honesty that comes out, I'm like: fucking what? And then whoever it's directed at just goes, 'Yeah, I see where you're coming from, I am a wanker.'"

Barlow arranged for a TV crew to document the recording of Progress, inspired by the Beatles' Anthology, apparently blithe to the fact that the camera crew's presence during the making of Let It Be famously soured the already fractious mood within the Beatles and hastened their demise. Williams didn't mind that the cameras were there – "Well," he says with mock-largesse, "I'm used to it" – but Orange "hated it". "I wanted to enjoy Rob, I wanted to enjoy the reunion privately. I didn't want me or any of us to be acting differently, because everybody acts a bit differently when there's cameras on. I don't know anybody who can be completely natural in who they are when there's a camera on them, and I wanted to have that process. I didn't want it to be captured on camera, but it was. Gutted."

They can't seem to decide whether Williams was asked to rejoin Take That five years ago. Barlow says he wasn't; Orange says he personally asked him, but Williams refused. Williams says he was on tour, heading towards a stint in rehab for addiction to prescription drugs and "didn't really notice until, you know, they sold 250,000 tickets for their tour". Certainly, initial attempts to get the quintet back together sound pretty agonising. For The Record ends with the other four waiting for Williams to show up in a hotel. He sent a taped message wishing them luck instead. "Smoke and mirrors," he says now. "It wasn't explained to me that way, you know, there's going to be four lads in a room wondering if you're going to turn up. The way it was presented to me was we were all giving messages to each other, so I sent the message. It was bit of a stitch-up job, to be honest. I mean, the words I spoke were the words I spoke – I didn't get stitched up with what I said – but I wasn't happy with the end bit."

Even so, Williams apparently talked a recalcitrant Orange out of quitting the Take That reunion shortly before the press conference to announce it, in November 2005: "I felt like there was no one else who would understand my fear and trepidation, my out-and-out terror, except him, so I reconnected with Rob," Orange says. "He laughed when I rang him. He was laughing his head off, going, 'What are you going to do, man?' "

When, on that tour, the five were finally inveigled into a room together in a Chelsea hotel, it went badly. "There was a lot of water not under the bridge," Orange says, "lying stagnant." And when the others tried to rectify the situation by leaving Williams and Barlow to sort out their differences, things went from bad to worse. "It was awkward," Barlow sighs.

"It was a bit like being at a wake with a family member you haven't spoken to on purpose for a long time," Williams says.

Another subsequent meeting in LA was equally strained. "I went down to their hotel and it was the same as Chelsea really," Williams says. "We all got in a room and I kind of got this force from over there, where Gaz was, you know, my eyes weren't going over there, but my whole chi was. And I came away and went back to my house. I knew the lads were coming over the next night, and I started writing the speech in my head of what I was going to say, make or break, to sort things out or not. I was fucking shitting myself because these lads had been together three years and they were all comfortable with each other. Anyway, I got to say my piece and it was terrifying. Then Gary's piece was said. And then we were falling about on the floor in the kitchen laughing next minute, arms around each other, pissing ourselves laughing. It was fucking brilliant. It really, really was. It was proper puking rainbows stuff."

"We had 15 minutes where we felt invincible and we were like, 'We've got to do this, we've got to do this,' " Barlow says. But Williams continued to procrastinate: "I'm very definite about stuff, and then not. We were definitely, definitely doing this, but then, you know, I spend a lot of time in the house thinking, 'I don't want to leave this house.'" Furthermore, he says, he had been "physically ill" throughout the campaign for his last album, Reality Killed The Video Star: "I had something that made me tired all the time – not as serious as ME. The reason I'm being guarded about it is because if I told you, people would go ha, ha. But it really fucking affected me."

Nevertheless, "after a bit of love and tenderness from the lads", he committed, and the recording of Progress apparently went without a hitch – "There was one argument," Williams says, "but it was like an argument on Valium." The album features a song, SOS, that details Williams' obsession with conspiracy theories and some of the more esoteric internet chatrooms ("You know the end of the world's meant to happen in 2012?" he chuckles, adding swiftly, "Luckily, I've had a word with my shaman and it's not going to happen"), and one called What Do You Want From Me? that sounds suspiciously as if it's dealing with fallout from Owen's private life – he checked into rehab in March after confessing to extramarital affairs – but Owen insists isn't. "No, it's not reflecting back on recent events," he says, those eternally boyish features momentarily looking strained. "It was written before then. You know, when you reach a certain point with anybody in a relationship? That same song could relate to the band." He frowns. "Not that I want to have sex with the band."

http://www.guardian.co.uk/music....on-tour