For a while, Gavin And Stacey star James Corden looked invincible - until his subsequent sketch show with Mathew Horne was panned and he discovered London's bar and clubbing scene. The father-of-one tells Sarah O'Meara how he turned it all around.

"The person I look back on, two-and-a-half years ago, I don't really recognise as me," says James Corden in a thoughtful, reflective voice, sounding nothing like his cocky alter ego Smithy from Gavin And Stacey.

Remembering times of partying, drinking, ignoring phone calls from his family and being rude to his agent, he's still embarrassed about letting the hype go to his head.

"I wasn't in AA or anything. I just got a bit lost. I was heartbroken and a little bit famous... and that's a bad mix," he says, momentarily allowing his childish grin to break through the introspection prompted by his new autobiography May I Have Your Attention, Please?

The past decade has been a "rollercoaster," the 33-year-old admits. After landing a part in West End musical Martin Guerre aged 17, he went on to star in ITV's Fat Friends (where he met future Gavin And Stacey writing partner Ruth Jones), was cast in the National Theatre's international tour of Alan Bennett's The History Boys, which ended in a film adaptation, and then created and starred in seminal comedy Gavin And Stacey, a series that garnered a level of public devotion not seen since the likes of The Royle Family.

For its 2010 finale, the Gavin And Stacey show he co-wrote with Jones pulled in 10 million viewers. Backstage though, as television's chubby golden boy explains in new book, he wasn't happy. And Corden fans probably won't need an autobiography to tell them why.

Riding high on a crest of professional success, when mediocrity hit it was a bitter blow. His sketch show Horne & Corden, debut film Lesbian Vampire Killers and even James Corden's World Cup Live- an apparently harmless ITV presenting gig - were labelled as drivel by critics. And Corden is nothing if not honest about why he failed to deliver the goods.

"Trying to write a TV show, or be in things and be good, and going out all the time, are mutually exclusive. You just can't do them both.

"You feel like you can because you're still handing in the work - it's just not very good. Not to say it's awful but it's not good enough."

As well as the rewards of fame, Corden was also struggling with being single for the first time, after his nine-year relationship with Shelley finished in 2007 and his Gavin And Stacey co-star Sheridan Smith (she played Smithy's sister Rudi) ended their "turbulent" affair two years later.

So Corden rented a north London flat with Mamma Mia's Dominic Cooper and his socialising took on an epic quality. "At one point, for about two weeks, all Dom and I had in the fridge was some vodka, a bottle of pink vitamin water and a Lindt chocolate bunny," he writes. Parties once or twice a week followed, with Cooper "smashing the life out of a ludicrously massive electric drum kit he had bought." The noise became so bad that Camden Council threatened to fine them £25,000.

"Lots of people go to university, get really drunk and wake up in bed with people they shouldn't... but I went straight into a West End show, was in a stable relationship and had a flat, and then slowly, those things disappeared," Corden points out, philosophically. Soon his conscience, and his family, came to make their feelings known. "I was aware I'd been on a rollercoaster but I didn't realise lots of people who cared about me had been on it too.

"It's only speaking to my mum now and she'll go, 'Oh my God, we were worried about you'. I'd drifted so far away from the boy they had raised."

After his parents made an impromptu visit, terrified by reports of him falling out of clubs and bars, their worried looks were enough of a rebuke.

"There were no 12 steps. It was as simple as saying I'm going to stay in and I'm not going to kiss anyone unless it could be 'someone'. Of course, I didn't always stay true to that but it worked on the whole," he smiles.

That's a huge understatement. Corden's now in a steady relationship with charity worker Jules, has the lead in One Man Two Guvnors, transferring to the West End this autumn, and is the father of six-month-old Max. "It was my birthday yesterday and me and Jules ate sushi and watched Breaking Bad. And we didn't even finished the second episode. The baby started murmuring, we were asleep by 9.50pm."

James Corden will sign copies of his autobiography May I Have Your Attention, Please? at Waterstone's in Bluewater on Thursday, December 8 from 12.30pm. Call 0843 290 8159. May I Have Your Attention, Please? by James Corden is published by Century and costs £18.99.