There really was only one actor who could play a young lovestruck Will Shakespeare on the big screen, according to Shakespeare in Love director John Madden. With a script to die for, there were plenty of contenders from the A list who would have given their right arm to star in the romantic comedy. So who, from the cream of American and British acting talent, inspired John to give him, and only him, this most succulent of plum parts? Step forward one Joseph Fiennes, brother of the more famous Ralph.

"Joe was the unchallenged candidate from a very wide search," says John, who also directed the acclaimed Mrs. Brown. "He just stood head and shoulders above the rest. He was the only person remotely believable as the man who wrote the plays. He has the romance, the humour, the wit, the energy, the intelligence. The part belongs to him. He was my choice, and I made it very clear that I didn't want to make the movie unless I could find the right person. Joe was the one."

All the more remarkable when you consider that this is only the 28-year-old actor's fourth film, coming after a small part in Stealing Beauty, he role of Laurence in the small British comedy Martha, Meet Frank, Daniel And Laurence, and the Tudor biopic Elizabeth ("I'm getting used to the tights," says Joe with a smile).

Scripts of the heartthrob and blockbuster variety will now be landing on his doormat with a resounding thud. Studios will be offering fees of telephone number proportions. He is about to become a star - whether he likes it or not. "I don't believe in the next big deal, I don't believe in the next hot thing," he says defiantly. "So many people have been hyped in that way that the phrase has lost its potency. I mean, there's another guy out there who is the next new hot thing and another who has been that for a while. There's a whole corridor full of us. The great thing is to be allowed to work, to do good work. That's the joy."

Joseph is remarkably open compared to his brother Ralph, who is a painfully reluctant interviewee. But Joe can still be very guarded at times - perhaps as a result of watching his sibling's experience with the media, especially after the tabloids focused on Ralph's love life. Ask him, for instance, whether he's married and you get short shrift. "No, I'm not. But I could be. I wouldn't tell you if I was. So I could be lying. After all, I am an actor..."

Then he begins to thaw. And it would be wrong to suggest that the his unfriendly - rather, he fears coming across like a bit of a luvvie.

"I try not to read the things that are written about me. I think there's something very dangerous about an actor when he speaks. However honest the journalist is in translating what he says, an actor will always come across somehow as a bit of an idiot, especially if he speaks passionately about his work. I mean, I can speak to you now, but once it's in print it just looks naff. I just think, "Oh shut up..." So I prefer not to have to look at it..."

He also has to contend with following in the footsteps of Ralph, who is eight years older, and Joseph can spot the Journalistic traps a mile off. "No, Ralph and I don't discuss acting when we meet," he says firmly. "It's very rare that all our family get together, because everybody is so busy, and when we do we usually talk domestics. I'm doing a bit of DIY on my flat in London at the moment, so we talk about that."

Joseph and his twin brother Jake have four older siblings. The family shared a somewhat unconventional lifes-tyle, moving frequently with their photographer father Mark and mother Jini, novelist and painter who died six years ago.

"I think I had a privileged yet strange upbringing," he says. "It was bohemian but it was also functional. We were surrounded by constant stimulus from my parents and their friends, who were actors, musicians, sculptors, whatever. In some ways they all have the same key - observation - and they kind of blended with each other.

"To me as a kid it was phenomenal and a great adventure. We moved 14 times and it was always a challenge to reinvent yourself at school. I know a lot of friends who were unhappy at school - they'd probably been to two schools in their whole life and you end up getting labelled, your identity comes from other people not yourself.

"But I relished our life. I gues it was good preparation for acting too. There is the gypsy element to living an actor's life and I definitely had that."

That constant stimulus has certainly had its effect: as well as Ralph the actor, there is Martha, the director, Magnus the composer and Sophie the actress. Last year Martha directed Ralph in a screen adaption of Pushkin's "Onegin", Magnus composed the music and there was a small part for Sophie in it too. "I wasn't in it," grins Joe. "Actually, I'm sure that they don't want to work with each other ever again..."

Joe's twin Jake has bucked the trend by becoming a gamekeeper. "He has a love of the country, which I share," says Joe. And there is a foster brother, Michael, who is an archaeologist.

Joseph left school at 16 to study art, but acting was always at the back of his mind. After a year, he was helping out backstage while big brother Ralph was out front. "He was just getting into theatre. I used to go to the National to see him and that was wonderful. I was doing youth theatre and really loved it - I just knew it was what I wanted to do."

After three years at the Guildhall School of Music and Drama, Joseph concentrated on the theatre, notably with the Royal Shakespeare Company. The stage is, he says, where he feels most at home and where he will always return.

"Really, film wasn't on my agenda. I made a choice to concentrate on theatre and there were times when I was in debt, because theatre pays so badly, and I would lust after a TV job just to pay the bills. But I stuck with theatre. In the end, though, it's the written word that I find deeply fascinating and compelling. I respond to the material, whether it's in theatre or film."

His reluctance to venture into films earlier does seem to stem from a genuine fear of being famous. In which case, he's in big trouble. After "Shakespeare in Love", it's going to be difficult to avoid him. And for him to avoid his fans.

"I think one has to try to keep an equilibrium between the myth of Hollywood hype and the reality of life. Every actor knows about Hollywood hype. I went from youth theatre to drama school and then out into the professional cattlemarket. The frightening thing is the power of the film medium, it pushes you to take on a persona which isn't you," he says. "People have said to me, "You've come out of nowhere." But look at most actors and I guarantee it's taken them years of hard work to achieve a certain level of notoriety, of respect. Those who do really come out of nowhere don't always survive.

"I don't get recognised on the streets," he continues cheerfully. "If I go on the Tube in London with a hat on my head, it's fine. I haven't to worry about recognition yet, but I guess it could happen. Actors are like a commodity and you have to try to live with that."

Whatever happens, he insists, he'll stay in London. Although he's already had "one or two" offers from Hollywood, Joseph is currently working on a small-budget British film, "Rancid Aluminium", about a man with a complicated love life who gets mixed up with the Russian Mafia.

On romance, he is guarded as ever. A six-year relationship with an actress ended last year and he is, apparently, on his own. But, as he said earlier, he could be telling porkies.

Is he a romantic? "I guess there is a romantic hidden in here somewhere," he smiles. "I hope there is. But don't ask me what the most romantic thing I've ever done is. I don't know. I do know the most romantic thing that someone has ever done for me. They cooked me pasta..."

He's easily pleased, this Mr. Fiennes. Either that or he's learning the art of keeping journalists at bay.

As a stage actor, and a classical one at that, the role of William Shakespeare was both alluring and terrifying. At first, he admits, he was rather intimidated by the prospect of playing the great man. "He's sacred ground for a lot of people. It's a great opportunity to infuriate them all!

"Strangely enough, I didn't do much research for this. I mean research is great," he continues, "but with Tom Stoppard's unique script it's all there, it's watertight. At first I did look at what the academics have to say about Shakespeare's life, but it's a can of worms. For every expert, I realised, there was another one with a different theory, so in the end I just closed the books and embraced Tom's script."

The role, he decided, wasn't about portraying an icon - more a young man trying to make his way in the world. "I never felt like it was Shakespeare but a guy called Will who was a bit of a hustler. Rather like a journalist, he's a reporter of the human psyche. He's constantly looking for inspiration and Gwyneth becomes his muse... Once you look at it like that it becomes a lot easier.

"We see Shakespeare as a writer of exceptional talent, but we also see him as a man. And as soon as I put on the tights I knew that! The love scenes show the passion and the love. It's very real and in that way the man is very real, too."