Gary Barlow says: "As long as our friendship is as close as it is, I think the world is our oyster, I really do."

The Thats are back and this time it's permanent. Robbie's in rehab, and Nigel Martin-Smith, the Manchester management maestro, is no longer in charge. But Gary, Jason Orange, Mark Owen and Howard Donald, now a man band, still look, sing and dance like Take That, the boy band that, a decade ago, nursed a generation of girls through puberty. And, as Gary notes, this time they're tight as a drum with no Rehab Robbie to threaten their equanimity.

But there are other irritations. "Always the f***ing same," says Gary, as we stand staring at a locked door in San Remo. We are in a courtyard packed with Italian cops, security, two minibuses and assorted hangers-on. Beyond the gates, the street seethes, mainly with girls. They screamed when our little convoy swept in.

"Sorry I upstaged you back there, Mark."

"No problem, Bryan."

The door stays locked for about five minutes.

"They always do this," says Gary wearily, "to give the paps a chance to get their pictures."

At last it opens and, to my utter bewilderment, we are rushed though the lingerie section of a department store. A few customers have the presence of mind to get autographs off Gary and Mark. Why are we here?

"Oh, we always go through some weird entrance," says Gary. "Usually it's kitchens."

Then we are in some windowless corridors, then a temporary radio studio with a large man with orange trousers and an orange scarf. There is a huge window looking out on a further sea of girls, most of them taking pictures of us with cameras and phones.

"Taka Thata!" cries the orange man.

The girls scream, the Thats wave. They do the interview, then their song Patience is played over the air and, outside, over the girls. They all sing along. To my amazement, my eyes moisten at the sheer harmless joy of it all.

Finally, we are in a tiny dressing room, about one-fifth of which is filled by the "rider". The rider is the artist's list of special contractual demands. Mariah Carey has butterfly accessories and a blue carpet. The Thats' demands are simpler: fruit, raw vegetables, mineral water, fruit juice and various rolls. Picky Jason doesn't like the look of the sun-dried-tomato fillings, but he zooms in on the bags of freebies, sunglasses and trainers. He puts on a pair of huge shades and ditches his battered old trainers for a pair of new white ones decorated with gold fleurs-de-lys.

"Needed them." He sprawls on the sofa looking self-deprecatingly cool. Everyone laughs.

They are in San Remo to appear at the music festival. This started in 1951 and has the dubious distinction of having inspired the Eurovision Song Contest. The Thats are only here to do one song - Shine, their second No 1 since their rebirth - but here amid the Eurotrash glamour, it's a platter that matters. Anyway, they're loving every minute. After a decade in the post-break-up wilderness, a decade in which the former That Robbie upstaged them all, the Thats are happy again; happy, in fact, beyond their wildest dreams.

Each one tells me that the wilderness years were hell - Howard considered throwing himself into the Thames, Gary was humiliated in America - and that, when re-forming was first floated by Mark, their first thought was it would fail. But it didn't. Thirty arena and stadium dates last year sold out, their new album, Beautiful World, is their biggest ever in the UK, and the two ensuing singles have both gone to No 1.

Robbie, however, is still the spectre at the feast. In the decade after the break-up, he shot to the top of the fame mountain while the others slithered to the bottom. He rubbed salt in the wound with some ripe abuse. They sort of made it up, but not really. Then he went into rehab - with a press release saying so - just as the Thats' comeback was to be sanctified at the Brit awards. I was at the rehearsals and the talk there was that he'd done it deliberately to rain on their parade. Officially, the Thats don't comment - "He has his friends and family," they solemnly told a San Remo press conference - but, unofficially, they find the whole thing creepy, if not suspicious.

"One side of me wants to send him best wishes," says Gary. "I blame everyone around him. If it was me going into rehab, you'd never know. I'd be so embarrassed. But this bloody big press release giving all the reasons why… It's a big coincidence, isn't it? So who knows?"

Never mind. What the remaining four have achieved is one of the greatest, most consoling comebacks in pop - great and consoling because there is something irreducibly nice about this band. This niceness is not an incidental attribute, it is an aesthetic truth, as important as Elvis joining the army or the Beatles seeing the Maharishi. I was, at the Brit awards, overcome by this niceness. After they rehearsed their performance of Patience, I joined them in their dressing room. Jason, Mark and Howard gathered eagerly around me - this is not something the average, not-nice celeb does. Only Gary seemed to be holding back. Mark was all smiley and pleased to meet me. This boy has charm squirting out of his ears. Howard was curious but quiet.

Jason was the most effusive. "You've written books, yeah? It's good to be written about by somebody that's written books."

"Yeah," said Mark.

I couldn't help it. I glowed.

But, before anatomising this niceness further, there is one crucial point to make about this post-Robbie, post-Nigel phase. The last time round, Gary took most of the credit for, and the royalties from, their hits. But on Beautiful World, there is only one writing credit on each track: Take That. The boys, having become men, are in this together. This is, in itself, an act of deep niceness. It was Gary's idea and, he says, it lifts a burden from his shoulders. "It's a genuinely co-operative effort. We've got an honesty this time."

Take That was put together by Nigel Martin-Smith, an all-purpose Manchester showbiz entrepreneur, in 1990 with the aim of producing a British version of the American boy band New Kids on the Block. He had identified a pop gap -Jason and Kylie were already in the past and the record labels were obsessed with dance music. The teens were being left out.

But the five boys he chose were more than just evidence of marketing acuity: they were a brilliant psychological construct. Gary was musically very gifted, potentially what Brian Wilson was to the Beach Boys, and, for his age, hugely experienced. He had done the clubs and became a maestro of old-school pop. "I was 20 going on 50," he says. Jason was a break-dancing painter and decorator, thoughtful, occasionally agonised and always curious to know what he might have missed. Backstage at San Remo, he asked me about Bob Dylan. The photographer and I ended up singing him Like a Rolling Stone as the That dancers jiggled about, adjusting their silver boob tubes and hot pants.

Mark had dreams of pop and football but left school to work in a bank. Along with Robbie, he was the youngest, and, from the start, the two were close friends and all-purpose gofers for the older members. Howard, vulnerable and quiet, was a YTS-trained vehicle painter. Robbie, the increasingly wild one, was barely out of school when the band was formed. This was, in short, a shrewdly balanced collective of very distinct characters. But they had three big things in common. Or four, if you accept Gary's interpretation. "As one we were so ambitious, so driven to be famous and successful. It's all we really wanted and we'd do anything to get there."

Howard dissents: "I never wanted to be famous or a pop star. Maybe it's a confidence thing. I don't put myself forward."

The first thing they had in common was that they were all from the northwest. Speaking as a northwesterner myself, their geographical origin is important. Their accents are still total peasoupers. They never say "my", they say "mi" as in "mi mam", and the lazy-seeming drawl suggests a familiar kind of blurry, ironic wonder is intact. The wonder is, of course, that of the provincial, and nowhere is more pig-headedly provincial than the northwest. Northwesterners can travel the world and remain, in essence, untouched. The Thats are still from a land of which Manchester is the capital city.

Ironically, the man who offered them the world is even more provincial than the band. All four of them tell me the same thing about Nigel Martin-Smith - "He got jet lag flying to London" - so when the boys really hit the global road, Nigel tended to stay behind.

The second thing they had in common was a strong family instinct. This is most pronounced in Jason. He was brought up in Wythenshawe among five brothers, a group he clung to after his father left home. Strangely, before the father left, the family became Mormons, another group to cling to. His father was, says Jason, subsequently excommunicated when he confessed to his affairs. The faith lingered on for a while and, in Jason's case, never vanished completely. "Just the idea of God and Jesus… I'm still questioning religion."

Do you believe in God?

After a long pause, he responds: "I don't want to answer that question."

He admits he transferred his sense of and need for a band of brothers to the band. "I think I have an insight into male group dynamics because of the way I was raised with my brothers, and I tried to impose that on the lads perhaps too much."

In fact, all the boys were looking to belong when they met Nigel. Whether from strong families like Gary or broken ones like Jason or, like Mark, they had drifted into jobs that did not reflect their deepest interests, they were seeking identities that would give them companionship and a distinctive place in the world.

Which brings me to the third big thing they had in common: Nigel. Gay and utterly focused on his New Kids on the Block formula, for Nigel the Thats were, in Jason's words, his "surrogate children". He used to say he was their mother, a role reflected by his insistence on keeping them pure. On-the-road couplings he could handle - though he did warn them that when they were famous, they would have to assess whether the girls would rush straight to the News of the World - but long-term romances he thought would threaten their pubescent fan base. Another interpretation hinted at by the boys is that he would be jealous.

All four of them said they were afraid of Nigel. He intimidated with his knowledge of show business and his conviction that a boy band must be the next big thing. Such was his power that the music he was expecting them to make was not an issue, even though, certainly for Jason, Howard and Mark, straight pop was not their thing. They were into dance or the big indie rave scene that still gripped Manchester. But Nigel offered a clear road ahead, an escape into pop.

"I just thought it was an adventure," says hip-hop-loving Howard. "I just thought I'd go with the flow, see what happens."

Mark, meanwhile, the smallest That, was simply cowed by the other members of the band. "One of the first things I thought was that they were all so healthy. Jason and Howard looked really strong compared to me. I used to go to a gym and do weights to build my strength up, but physically and talent-wise, I didn't feel like one of the strongest members of the band."

Ominously, Jason was the most ambivalent about Nigel. "Take That was Nigel and, from the word go, it was difficult between us. I'd never met a man like him in my life."

Young and - apart from Gary's many clubland gigs and Jason's dancing, which had got him a role in the TV show The Hitman and Her - utterly inexperienced, they adopted the pop identity offered by Nigel. But for two years it seemed like a terrible mistake.

The boys had a whale of a time building local fan bases, careering round the north in a hired van and chucking cards advertising themselves out of the windows. It was exhausting. "We were absolutely f***ed," says Howard, "We were doing four 35-minute shows a day. It was more than we do in concerts now."

Those two years made them professionals, but, more importantly, it cemented their relationships. "We became a band," says Mark, "a close-knit unit. By the time we broke through, we were comfortable with who we were."

But their first three singles did almost nothing, and the big labels remained uninterested. All the songs had been written by Gary. Nigel had not intended this and had been thrown to discover that Gary had a catalogue of material to offer.

"I gave him a demo tape," says Gary, "and I could tell by the way he took it off me that he wasn't really interested in the idea of original songs. He just put it to one side on his desk." That incident signals an important Gary characteristic: he is very observant, a gift honed by his apprenticeship seducing initially bored and sceptical club audiences. He constantly watches how people are reacting to him.

And so, for the fourth single, they recorded, at Nigel's insistence, a cover. It was It Only Takes a Minute, a 1970s hit by the US soul band Tavares. Gary was not too upset by this - he had, he admits, huge self-confidence and a conviction that his own writing career would eventually be a success - and they all knew it was their last chance. It came out in 1992 and it was a hit.

From then until Robbie left in July 1995, the Thats found themselves cruising the big time as the most globally successful British pop act since the Beatles. Their success was generic - sex, some drugs and lots of rock'n'roll - but for one important aspect. They never stopped being loved, being seen as nice and unthreatening. There was no Sgt Pepper, Beach Boys' Pet Sounds or a Dylan-going-electric moment when they became something weird and difficult, alienating parts of their initial fan base. Certainly, they swung away from being a covers band to being performers of Barlow songs, but they always remained pure popsters, living, as David Beckham would put it, the dream. In Gary's autobiography, My Take, he recounts a pop epiphany when they befriend Elton John and see his house - a palace of treasures, a monument to all that pop longevity had to offer. "As we pulled through the gates," wrote Gary, "it was as if someone had put a huge bolt of electricity through me. He had hundreds and hundreds of gold discs, while at this point we had two."

This kind of longevity was what they had in mind. Apart from Howard, all of them seemed to think their life at the top could go on for ever. In fact, this was always impossible. Five unformed boys were not going to become men and remain complacently either together or under the control of their provincial svengali. Nigel had seen this from the beginning. "One day," he told them, "you'll hate me."

Robbie's erratic behaviour was the first sign. He was turning up drunk at morning rehearsals. This alarmed Jason in particular as, at one point in their act, Robbie cradled his foot and flung him into the air. A less-than-focused Robbie could break his neck. More poignantly, Robbie burst the bubble of the boys' belonging. He brought along a band of friends he called the Diamond Dogs. Tensions mounted and, finally, Jason confronted him, demanding he get back into line. He still feels guilty, but Gary insists he shouldn't. "If it hadn't been him, it would have been one of us."

Robbie stormed out. They expected him to come back. But it was a single image of dislocation, of a bubble burst, that convinced them he'd gone for good. He was seen on a yacht in the south of France with George Michael and Paula Yates. All the boys mention this moment. "Once the strangers were let in," says Gary, "having their say, we knew that was it, we knew he was gone."

But the four of them toured on. Then Nigel made a fatal mistake. He gave them four weeks off over Christmas. It was their longest holiday and it gave Gary time to think. If Robbie was going it alone, so could he. He came back to tell the boys and, in February 1996, Take That announced their dissolution.

What followed for all of them except Robbie was a descent into show-business hell. Gary, expected by everyone to be the solo star, endured a long, humiliating crash culminating in a private show for the mega-producer Clive Davis which did not earn him a single clap. He put on four stone and became the first Fat That until his level-headed and very northwestern wife, Dawn, made him see a doctor. Howard contemplated suicide and then his own solo career, which fizzled. He returned to being a DJ. Mark, always the most popular with the girls, had more success with two No 3 singles, but then a poor album showing led to him being dropped by his record company. In 2002 he won Celebrity Big Brother, an achievement that, if anything, only highlighted how much he had lost. Jason took the break-up with the most equanimity, retreating, initially, to the Lake District. He tried acting but found he could not stand the auditions. He then took college courses and travelled the world, seeking, as ever, to remedy the defects in his education. He is a man with a perhaps excessive sense of respect.

"Is it okay if I call you Bryan?" he asks.

What else are you going to call me?

"Mr Appleyard - you're older and you've written books."

And yet, ironically, by 2005 they all seemed to have achieved some sort of stability. Three of them have children, not Jason - "I don't think I'm grown up enough. Getting there." Gary was having some success as a producer and had abandoned his Elton John phase by selling about £2m worth of stuff he had acquired and moving from his massive house near Chester to London. Then came the ITV documentary For the Record. This was a substantial and highly successful piece of work that prompted speculation that they would get back together. And, slightly drunk at the time, that is what they decided to do. "Good ideas," says Howard, "come to you when you're pissed."

But Jason had a condition: no Nigel. "I had a lot of power taken away. I lost myself in a way. That battle to keep us as a brotherhood, I lost that battle. I'm on my way to winning it this time. That's why I'm so pleased."

All agreed with Jason that there was no way they could return to the old hierarchies with Nigel at the top, Gary beneath him and the remaining three somewhere below. They became a co-operative with Mark's manager, Jonathan Wild, as an amiable and hard-working fixer.

They were stunned by the response to their return. The packed stadiums and hit songs returned as if they had never gone away. East 17 and All Saints have tried this and, so far, failed. What is it about the Thats?

The boys don't really know. Indeed, they genuinely were expecting to do no more than a few theatrical venues and then to sink back into relative obscurity. Instead they have a three-album deal with Polydor - not BMG, the label that abandoned them - and a touring and recording schedule that looks distinctly relaxed. And they're not for the time being intending to touch America with its musically homogenising demands, which drove Gary to compulsive eating. They are their own men, not boys, and they're going to do it on their own terms.

When I press them to tell me what's so special about them, they talk about nostalgia and the way fans saw them as individual characters rather than just a pop unit. They're right on both counts, but there has to be something more to explain this phenomenal surge of support.

I am still mulling this over as we eat octopus in a superb San Remo restaurant before they go on to do Shine. It's their niceness, of course. They are unbelievably easy to be with and, on stage, that makes them seem approachable, even touchable. When I saw them rehearse Patience at the Brits - in front of, I was solemnly told, a screen made of Swarovski crystals - I saw something else. They were better than before, much better, in control, a proper band of brothers.

An hour or so after the octopus, I give up thinking. There are few things that can make one's chest swell with patriotism quite as effectively as Italian TV and pop. They are the worst at doing what we do better than anybody.

Backstage I watch this in dismay as the Thats bounce nervously on their toes, Mark inhales Olbas Oil to clear his nose, and their dancers adjust the silver helmets that have been added to their costumes. Then they go on and wow us all with Shine. They are just so damned good at doing pop. Their act is a unique combination of the slick and the lovable.

No question, the Thats are back because they're nice and they put on a superb show with Gary on piano, Mark singing the lead, Jason break-dancing and Howard inward and understated as ever. "It is what it is," says Gary with Zen-like satisfaction as they come off.

So get well soon, Robbie, but, as the band they really wanted to be once sang, let it be. Let the rest of us take that and party.

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