Watching Gary Barlow on The X Factor, which reaches it’s finale this weekend, mentoring and dishing out advice to young hopefuls, it’s hard to remember a time when he wasn’t at the top of his game.

But as recently as 2005, the year the documentary Take That: For The Record aired, prompting the group's reunion almost a decade after they’d split, he was a faded force.

It seems ludicrous now, but when he, Howard Donald, Jason Orange and Mark Owen announced they were getting back together, there were sneers all round. The idea that the foursome could pick up where they left off, without Robbie Williams, who’d left the group prematurely to become one of the country’s biggest-selling solo artists, seemed impossible.

One listen to Patience, their 2006 comeback single, and the sneers stopped.

But why the initial doubt? Songs Barlow had penned, after all, had been among the biggest hits of the Nineties, breaking chart records left, right and centre.

His solo efforts during the group’s break, though, hadn’t been so successful...

His debut Open Road capitalised on his reputation as the “real talent” in Take That, selling almost three million copies and spawning two No 1 singles. But with his follow-up, Twelve Months, Eleven Days, things spectacularly ground to a halt. It peaked at No 35 and fell out of the Top 100 a week later.

“I was in a rotten place back then,” Barlow says now.

“It was written by committee, that album, with [producer] Clive Davis in the US telling me who I should be and who I should work with, then the UK label telling me something different over here, and there’s actually very little of me on there.

“I promised myself this time around that I wasn’t going to listen to anyone else, or be swayed,” he adds. “The first time the label heard the [new] album was when I’d finished it.”

The new album is Since I Saw You Last, his first as a solo artist in 14 years. The title track, he says, is one of the most literal things he’s ever written, summing up exactly where he, Williams, Orange, Howard and Owen were, all that time ago.

“It’s about where we are today, too,” he continues. “It’s a celebration, saying that even though all that stuff happened, it led us back here, to this great place we’re at now.”

There's a duet too, with his old pal Elton John.

“I’m in contact with him a lot, we’ve known each other about 20 years,” he says, in a way that hints he still can’t believe he’s friends with his idol.

They see each other about four times a year, and most of their communication involves exchanging music recommendations, but when Barlow had a song he thought they could sing together and sent it over, within 10 minutes he’d had an answer.

“He was on the phone, said it was a smash and wanted to record it as soon as possible,” says Barlow. “Three weeks later, we were in the studio playing the piano part together, recording the vocals in the same room. It’s an old-fashioned duet in that sense, two people in the room together, and it was brilliant.

“He's my idol, Elton, he’s the reason I sat at the piano in the first place, so to be in a studio with him as an equal is incredible. The funny thing is, the song’s about that mutual respect.

So what's different now, compared to 14 years ago? Barlow, who is rumoured to have a home in Alvescot, West Oxfordshire, puts it down to self-confidence, and being happy.

He doesn’t believe he’s become a better songwriter since then and still, despite the 50 million sales, has sleepless nights worrying he’ll never write another good track.

“I’m so lucky to find these melodies,” he says. “I never feel like I was put on this earth to write songs. Never.”

Acceptance seems to have played a part in Barlow’s renaissance, too - he admitted in his autobiography, Gary Barlow: My Take, that he once saw the other members of Take That as his backing act, but now realises that he wouldn’t be where he is without them, and cherishes it.

“I took Take That for granted, we all did, and now it’s come back to us, we realise how precious it is,” he says. “I include Rob in that, it’s his band too. The band is for us all to take care of for the next 20 years, or whatever. We can leave it and do other things and come back to it, but it’s my number one priority.

“I see the solo album as a lovely little hobby for a year, and it’ll mean I can release some music and do a tour, but the main job is always going to be Take That.”

It was the string of live shows he played this time last year, which included his New Year’s Eve gig in Oxford, that prompted Since I Saw You Last in the first place.

“We extended that tour three or four times, because we were having so much fun,” he recalls. “After getting home, I thought there might be a record in me, put my head in that space for a few weeks and wrote three or four songs.”

Another, much bigger, tour is set for next year. While not on Take That’s scale - their Progress tour saw an unprecedented 1.34million tickets sold in 24 hours - Barlow will be playing arenas all over the country.

“There’ll be a bit of production, but mainly it’ll be me and the band, very music-based. Put it this way, there won't be any 60ft robots, elephants or unicycles,” he says, referencing some of Take That’s stage props.

The group is set to reconvene in January to start work on their seventh album. Right now, it's unknown whether Robbie Williams will take part, although the invitation is there.

“It all needs organising,” says Barlow. “We’ve all got families and there are lots of things that need moving around to make it happen.

“I’m really, really looking forward to getting back with the guys though,” he adds. “It’s our first [record] in four years, and that’s daunting and exciting. I’m very excited about my tour too. So yeah, it’s going to be one hell of a year.”