Zac and Vanessa on High School Musical 3

Unless you have been living in a cave for the last week, or in detention, you won’t have escaped the buzz around Disney’s High School Musical 3.

What started out as a modest TV movie back in January 2006 has fast become a global phenomenon, with its first theatrical release smashing UK box office records for advance ticket sales weeks before it’s even on the silver screen.

And then there was the London premiere, where thousands of young fans skipped school and queued for hours to get a glimpse of the show’s fresh-faced stars Zac Efron, Vanessa Hudgens and Ashley Tisdale.

For anyone who doesn’t have HSM-obsessed children, it’s hard to understand the fuss about the squeaky clean musical extravaganza.

It’s almost Grease-lite - no smoking, swearing or sex, but plenty of colour, catchy tunes, soppy lines and spine-tingling dance sequences.

Vanessa, who plays one half of the romantic leads Gabriella and Troy (played by Zac), sums it up neatly: “Kids can relate to us and our characters.

They’ve been to school with the Troy, the Gabriella and the Sharpay (Ashley) and they look up to us in a sense because it is a world where there is no sex or drugs or violence, it’s just a movie that makes you feel good.”

The chocolate box-pretty 19-year-old is sipping tea in an elegant London hotel suite the morning after the premiere.

“I got butterflies in my stomach, it was just the craziest feeling,” she says of the red carpet madness.

“And it was definitely more nerve-wracking watching it with the fans. We were waiting for everyone to laugh, like ‘come on, come on!’”

“You go into a dream state,” 20-year-old tween heart throb Zac tells me later.

“Premieres are one of the few opportunities we have to meet our fans and I at least try to make eye contact with most of them.”

The original High School Musical follows the well-known Grease/Romeo And Juliet love story, as basketball jock Troy and beautiful maths geek Gabriella fall for each other against all odds and land the lead parts in the school musical.

The second instalment moved the action to a country club in the summer holidays where the devious Sharpay conspires to steal Troy from Gabriella, but all ends happily with a Troy and Gabriella duet and their first kiss.

Senior Year now sees them back at school, where they are torn between their love for each other and their friends, and the all-important college choice.

“I really love watching the characters grow,” Vanessa admits.

“In the first movie they meet, in the second they get a kiss and in the third movie, I feel like you really get to see them fall in love. It’s just this sweet, respectful, innocent love they have for each other and I love watching it.”

In another sprinkling of Disney magic, the two cast members have also fallen for each other and were recently pictured cosying up at a Parisian cafe.

Is it tough for Vanessa to kiss her real-life love on screen?

“It is,” she says with a shy smile.

“When I was about 11, I was in my acting class and my teacher said ‘you’re going to have to do this someday’ and she gave me that scene from My Girl where they kiss and I don’t think I’ve ever been more embarrassed in my life, but I thank her now because I have to do it. It’s a really great part of the story, though, very sweet and romantic.”

But back to the more serious matter of those tough Senior Year choices...

“The pressure is building and you don’t know what you’re going to do with your future, where you’re going to go to college, or what you want to study and you don’t know what’s going to happen with your relationships,” Zac explains.

“A lot of kids don’t make the choice that Troy does, to listen to himself and try and follow his heart, so I admire that.”

For Zac especially, art has mirrored reality.

“Troy is choosing between athletics and performing and I actually did have to choose between pursuing academic full-time, going to college, or sticking with High School Musical and trying to act.

“This seemed like the more interesting choice... it seemed like college would always be there, but you can’t say for certain that you can take a break from acting and always have the same opportunities that you would if you had stayed in it.

“I’ve always pictured my life going through college at some point,” Zac continues, “and I’ve studied hard to get good grades, believe me. As a senior, I was accepted to USC and UCLA for their film and theatre programmes and I had the option to study about filmmaking and acting or actually go off and learn while doing it. I feel like I’m learning 10 times what you could behind a desk.”

Gabriella, meanwhile, gets accepted to the prestigious Stanford University and is invited to start early, which means she could miss the high school prom and musical.

“She’s really torn up, she doesn’t know what to do because she feels like she’s at a place in her life where she finally fits in,” says Vanessa.

The starlet missed out on graduating from high school in real life because she was tutored at home, but she says the final big graduation number made up for it.

“It was my first time to wear a cap and gown, so that was really exciting and I was graduating with my class, the cast, who are my best friends. It meant a lot.”

When Dirty Dancing choreographer and director Kenny Ortega called cut on the final scene, there wasn’t a dry eye on set.

“Kenny made his speech and it was very motivational and we couldn’t help but cry,” says Vanessa.

“The tears were just rolling down our cheeks and I’d look at Ashley and she’d be bawling, which made me cry. It was really emotional.”

While High School Musical may have come to an end for the seniors, a younger generation of characters from the year below look set to continue the franchise. Would Vanessa want Gabriella to cameo in a High School Musical 4?

“I don’t know. I’ve heard rumours about it, but I haven’t been approached, so I don’t really know anything about it. Right now I’m just excited for the fans to see this one.”

As the publicity tour continues on to Los Angeles, the cast members will soon go their separate ways, but Vanessa’s not worried about losing contact.

“We’re all best friends and we live within a three-mile radius of one another, so it’s not like we plan to see each other, we KNOW we’re going to see each other.”

Vanessa, Ashley and Corbin Bleu, who plays Troy’s best friend Chad, have all released albums in the US since their HSM debut, but Zac made a conscious decision to stick with acting.

“I think it would have been very fun to have a music career, but I can’t say at the end of the day that it would be genuine. Music has been a hobby my whole life, but it was never a passion, so I don’t know if I deserve to be doing that,” he says, sounding more mature than his 20 years suggest.

Zac’s focus on acting has paid off, with upcoming roles in Me And Orson Welles, alongside Clare Danes and 17 Again, with Friends star Matthew Perry.

He’s also set to collaborate with Kenny Ortega again in a remake of the 1984 classic Footloose, playing the lead role made famous by Kevin Bacon.

“It’s a different style of movie from High School Musical,” says Zac.

“It seems older and I see a lot of potential in the character of Ren.”

Is he at all daunted by the task of revisiting such an icon film?

“That’s the challenge,” he admits. “We’re trying to figure out the right way to approach this, we wouldn’t want to remake the film and we wouldn’t want to sacrifice... there’s a lot of ways you could mess it up,” he says, laughing.

“We’re trying to put a fresh spin on it and make it our own and we’ve made progress lately.”

Vanessa has just released her second album Identified in the States and will be back on screen next spring as a high school misfit who makes a rock group with the popular girl in Bandslam.

“It was a lot of fun, because it’s a different character for me and I’m really excited for the fans to see a different side of me.”