Hayden Panettiere: The Heroes star is leading a far from ordinary teenage life

Hayden Panettiere is the poster girl of hit television show Heroes. The plot of the series about ordinary people who suddenly discover they've got superpowers could almost work as a metaphor for the life of the 18-year-old. Overnight she was thrown into the global limelight by the phenomenal success of the show. Every word and action of this girl from upstate New York became newsworthy, including her wardrobe, the men on her arm and, perhaps more surprisingly, her politics.

In Heroes, which returns to BBC2 tonight, Panettiere (pronounced Pah-nuh-tee-air-ay, like the Italian for "baker") plays Claire Bennet, a 15-year-old cheerleader, who, in the first episode, discovered that she could heal instantly from any injury. The indestructible high-school student is forced to hide her ability from her peers and maintain a relationship with her father, a man who is keenly interested in people with special powers.

The first series won plaudits and awards but the start of the second series was met with a backlash when it aired in the US. Fans complained that the show had become lacklustre, the new characters were uninteresting, the trademark episode cliffhangers were noticeable by their absence and the story was unfolding too slowly. Show creator Tim Kring even went on record to apologise for the mis-steps and just as the season got back on track, the writers' strike ensured that the second series only had 11 episodes rather than the expected 24. Arguably it was a blessing in disguise.

However, just as interest in the show was beginning to wane, media interest in Panettiere went into overdrive as it emerged that she was dating her co-star Milo Ventimiglia. The news was met with consternation among her fans, with a consensus that the 12-year age gap between the pair was too large.

The blonde teenager has complained about the judgmental attitude of the criticism, but believes that she is now mature enough to handle it. One of the reasons for this is a holiday to Europe that she took with Ventimiglia and fellow cast members Jack Coleman and Adrian Pasdar: "About five days after I turned 18 [in August 2007] I took off to Europe with them. It was the first time that my mother hasn't travelled with me and we went to Munich, Paris and London. It was such a different experience being on your own and it just changed me dramatically. My mom says that one person walked on that plane and another person walked off."

She talks of having a family at home and a family on set. She describes the cast of Heroes as being her surrogate fathers, brothers and sisters; revealingly, there is no room for a surrogate mother. Her mother is Lesley R Vogel, a former soap actress who put her daughter into her first commercial when she was just 11 months old. At the age of four, Panettiere had landed her first part in a soap, and by the time she was nine she had appeared on Jay Leno's talk show. Aged 10, she was nominated for a Grammy Award for Best Spoken Word Album for Children for A Bug's Life Read-Along. She has sung songs for soundtracks including Bridge to Terabithia, and later this year her debut album is due to be available for download.

It seems that it's impossible not to talk about her wardrobe. When we meet she is wearing a blue Cynthia Rowley dress that, given its length, could easily be mistaken for a T-shirt. Her face is splashed with ready-for-television make-up and her hair is immaculately curled. She looks like the archetypal all-American prom queen. She is being spoken of in the same breath as Lindsay Lohan and Mischa Barton. However, unlike both those stars, who have both been arrested for drink-driving, Panettiere's arrest record is one that she is proud of.

On 31 October 2007, she was part of a group of protesters involved in a confrontation with Japanese fishermen. The group tried to disrupt the annual dolphin hunt in Taiji, Wakayama, by swimming towards dolphins that were being herded to a cove where they could be killed. In the confrontation, Panettiere paddled out on a surfboard before being forced back to shore as the fishermen used their boats' propellers and harpoons to block the protesters. On the beach, television cameras caught the actress in tears before the group of surfers headed straight to Osaka Airport and left the country to avoid arrest by the Japanese police.

The protest established her as the poster girl of the Save the Whales Again! campaign. She recalls: "I was absolutely beside myself the whole time. They wanted to arrest me, but it created such a wonderful stir in America and around the world that it was the biggest step forward we've ever had with the problem. At the end of January, I spent four days in Washington DC visiting the embassies of Japan, Norway and Iceland, the whaling nations. I spoke to the foreign minister of Japan and I think that they've lifted the arrest warrant, because I was at the embassy and that would have been interesting locked in a jail cell below the embassy in DC, but he welcomed me back so unless it's a trap I think I can go back to Japan now."

She recounts the tale with a glint in her eye: "He was so polite, respectful and kind and told me: 'You are the most welcome guest that I've ever had.' I was like, 'Shit, really! Thanks. I don't know how much I believe you, but thanks.' We spoke about how Japan looks at Sea Shepherd as if they are a terrorist organisation, and about how whaling can be stopped."

Whether she will turn out to be the Hanoi Jane of her generation or not, American politicians are as eager as the whaling nations to get her on side. I'm struck by how nonchalant the actress seems as she talks about being tapped by both Barack Obama and Hillary Clinton: "I've had conversations with both of them. Actually, it was with Obama and Chelsea Clinton rather than her mother. The reason I was having meetings with them was to ask about their opinions and views on whaling, which dramatically impacts my opinion on who I vote for." Only just old enough to vote, the actress would not divulge which of the two camps won her over.

The Heroes star is even turning the media infatuation with what she wears into a way of helping save the whales. She has set up a website (www.panettierecloset.com) that sells clothes and accessories from her wardrobe, with the proceeds donated to animal-rights campaigns. When purchasing from the site it will pay to remember that the actress is only 5ft 1in.

Her film career is about to take off, too. She will soon be seen in Fireflies in the Garden, in which she stars alongside Julia Roberts, Ryan Reynolds and Emily Watson. In the family drama, Panettiere appears in the flashback scenes playing the young incarnation of the no-nonsense character that Watson plays in the present. Fireflies' director, Dennis Lee, has no doubt about her star quality, "Hayden is spectacularly talented. People know her through Heroes but she is the real deal. I'd love for people to understand that and not lump her in with her generation of actors who tend, for a lack of a better phrase, to get themselves in trouble. She has her head on straight."

Whether or not she is the most talented actor of her generation is a moot point; what is in no doubt is that she is the most dynamic teenager to have come on to our screens in a long time.

'Heroes' starts tonight at 9pm on BBC2; 'Fireflies in the Garden' will open later this year