THREE years ago, shortly before the first Inbetweeners film was released, Simon Bird, Blake Harrison, Joe Thomas and James Buckley insisted that the movie marked a final goodbye to the socially inept teenagers we'd all come to love since their debut in 2008.

That film became the highest earning British comedy of all time. And now they're promoting the sequel. It's not for the money though.

"If it was about the money, we'd have brought a sequel out much quicker," says Harrison, 29, who plays the lanky, gormless Neil.

Thomas, 30, who plays the slightly neurotic and often lovelorn Simon, agrees: "We'd be on about [film] four by now."

"We had no idea it was going to be as successful as it was," adds Bird, who plays pompous, former-briefcase-toting Will. "I think personally, for ourselves and for our careers, we wanted to go on and do other things and not get tied down by The Inbetweeners."

And that's what they did, for the next two years. "It was only that people didn't stop asking us whether we were going to make another film," continues Bird, who turns 30 this month.

"Yeah, there was still this demand," adds Buckley, 26, also known as pathological liar Jay. "Every day, people were coming up to me or tweeting me, 'Please do another film'. If it wasn't for the fans, this film wouldn't have been made."

Although Bird and Thomas, who met at Cambridge University, have since collaborated on the First World War-set comedy Chickens, they've all missed working as a foursome. "But that's not a good enough reason to make people watch [another movie]," says Buckley, who's become a dad of two since the first film's release.

However, the show's creators and writers, Iain Morris and Damon Beesley, had been busy working on another film script. "When we saw how funny it was, then everything changed and it became a no-brainer," admits Bird, who married girlfriend Lisa Owens in 2012.

So what fan fans expect from The Inbetweeners 2?

Set six months after the last movie, it sees the boys head Down Under.

"Jay's gone off to Australia to stay with his uncle and the other three lads are in Britain having quite a rubbish time of it," reveals Harrison. "Neil is working but he really misses his best mate, and the other two lads are at uni but not necessarily having a great time."

Then Neil receives an email from Jay saying how brilliant Australia is. "Even though they know he may be slightly exaggerating the truth, they think it's got to be better than what they're doing and head off," explains Harrison - and in great cinematic tradition, there's an element of a road trip.

It's less romcom-y than the first one," offers Bird. "It's more about the four of them. The Inbetweeners has always been about that group of friends."

This time round, Morris and Beesley decided to step up to the challenge and direct as well, something Thomas likens "to two kids being left in charge of a classroom".

"It was crazy," Bird says.

"They've always set up this attitude on set that if it's funny just do it, but there's normally a director in place to pull on the reins ever so slightly when things got out of control. So when Iain and Damon took over the reins, it was like the lunatics have taken over the asylum," adds Harrison.

As hard as it might be for the lads, and their many fans, it would seem this really does mark the end of The Inbetweeners' journey. As Harrison puts it: "The comedy comes from their ignorance and naivety, and if you follow the characters into their late twenties, that kind naivety is almost unforgivable."

It'll be tough to say goodbye though.

"I think it's a nostalgic show in some ways, because people look back to that age as an age of innocence," says Thomas. "There is something of that which Iain and Damon have managed to capture in these characters.

"There's nothing too threatening in The Inbetweeners' universe," he adds. "But at the same time, there's nothing too impressive either."

n The Inbetweeners 2 (15) in cinemas now