Patrick Dempsey plays charming billionaire Jack Qwant in Bridget Jones's Baby. Credit:Giles Keyte After 10 years and 250 episodes as neurosurgeon Dr Derek Shepherd on TV series Grey's Anatomy, which he left in 2015, he has returned to the big screen as a charming American enamoured with the much-loved heroine of imperfection Bridget, now 43. Bridget, played by Renee Zellweger, is still single and living in the same London flat but successful at her TV producer job and triumphant with weight issues. Her romance with Qwant is swiftly followed by a dalliance with former fiance, and now about-to-be divorced, Mark Darcy, again played by Colin Firth. Bridget discovers she is pregnant but is unable to name the father. Should she shack up with the well-adjusted and keen Qwant or the frosty but heart-swelling Darcy? First, though, racing.

Patrick Dempsey and Renee Zellweger in Bridget Jones's Baby. Credit:Susie Allnutt "It's intoxicating," Dempsey says. "You're pushing yourself past places you never thought you could go. The ability to suffer is what makes the great drivers really great. There is just a gift behind the wheel to go quickly and a beautiful dialogue when you're racing someone for position that is unlike anything else. "I mean everything else is boring in comparison. It's literally life and death. It's a heightened sense of life and, once you get caught in that, you never want to let that go. Manhandled: Colin Firth, Renee Zellweger and Patrick Dempsey in Bridget Jones's Baby. "I don't want to sound trite, but you want to be a part of the machine, that there is no separation between you and the car. It's all I wanted to do since I was a kid. I fell into acting."

Dempsey reached great heights behind the wheel, winning the Fuji round of the 2015 FIA WEC and coming second in class in the prestigious 24 Hours of Le Mans endurance classic. Patrick Dempsey played Dr Derek Shepherd for 250 episodes of Grey's Anatomy. "Japan was a transformative moment for me, personally, because I had set out to have specific goals, at great cost to my family. Because my wife was like, 'This is too much. You've got to pick. You can't do it and we're not going to travel. It's too much.' "It's an incredible sport and I would love to do nothing more than that. But it's all-consuming and I have three children and I don't want to give up that moment in time because they will be out the door and gone before you know it." Dempsey reduced his racing commitments in 2016 but his team, Dempsey-Proton Racing, continues to compete.

"Had I not had that success last year it would have been harder to step back," he says. "Racing is my true self." Stepping into the third film instalment of Bridget Jones' life is a big ask for an actor, but Dempsey is clear on why the character resonates with women. "I think it's incredibly challenging for women these days because there is so much pressure on them," he says. "I see it with my wife who is balancing a career and being a mother, being a wife and being herself. "It's very hard to do all those things and still be yourself, still find time to claim what you want separate to that." Dempsey has three children, twin nine-year-old sons Sullivan and Darby, and daughter Talula, 14, with wife Jillian.

"It's 'How do I be a good parent?'. You have to constantly keep working on that. When you're living in a town, and a business [like Hollywood] with the morals, well, you know. "How do you keep your kids grounded? How do you keep yourself grounded? It's a challenge." Dempsey says he would move out of Los Angeles in a minute but prefers being close to his work base. "Otherwise you're completely forgotten," he says. "No, that's crazy. But it's a tough business. "I would live all over really. Probably I would go back home to Maine. Live in the country, for the kids. I think, for the boys, they need to run free.

Helen Fielding, the author of the original Bridget Jones newspaper columns, books and screenplays confirmed on Tuesday that a Bridget Jones's Diary musical is in the works. "I'm really excited about the idea of a musical," she said on ITV breakfast show This Morning, adding that it would appear in the next few years. "Its very spontaneous, the theatre. I've written it. It's happening." Dempsey says a fourth Bridget Jones film is a possibility, based on the reaction to Bridget Jones's Baby. "What I would love to do in my career now is have the feeling that I've had in the car when I'm working [in acting]," he says. "In my career I have not really achieved what I want and what I feel I can do and where I would like to go. "Bridget Jones was the right next step after Grey's and I'm letting people know I've not quit acting.