Like any new mum, Minnie Driver says that it has been a struggle to return to work, but getting back to her day job brings its own particular challenges. “I made one film, Motherhood, when I was heavily pregnant and then two more afterwards. My entire pregnancy and two years post-birth will be on the big screen,” the actress says. “Flabby stomach and giant boobs for all to see.”

It has to be said that it came as a surprise when Driver announced on Jay Leno’s chat show in March 2008 that she was pregnant — no one had known that she was even dating. Having been stung by several messy public break-ups, including John Cusack and Matt Damon, she has learnt to keep her love life strictly under wraps. To this day, she has not revealed who is the father of her 17-month-old son, Henry. All she will say is “he’s English and in the same sort of business, and he lives in California. Everybody is cool with the situation.” Throughout the interview she refers to him as her “partner”, often with the prefix “great”, but from what she says she hasn’t actually seen him since November.

It would be understandable if her views on relationships, fidelity and marriage had been coloured by the fact that her mother, Gaynor, was her father Ronnie’s other woman. But that didn’t stop the actress’s overwhelming desire to be a mother, and, despite a rocky first trimester, her pregnancy went smoothly.

“I had terrible, terrible morning sickness for the first four months of my pregnancy, but I soldiered on, and I walked and practised yoga until the day Henry was born in September 2008, in Los Angeles.”

I ask her if she’d like more children. “Growing up, I thought I’d have at least five kids,” says Driver, who turned 40 at the end of January. “I’m surprised I have only one; I really want more. It was never my intention to leave it until I was in my late thirties, but it was never the right time, right place or right person. Too many women put it off until everything is in place, but there’s never a perfect time, is there?”

Motherhood has also helped Driver to put the public highs and lows of her career into perspective. After her critically acclaimed performance in Circle of Friends in 1995 and then two years later in her Oscar-nominated performance in Good Will Hunting, her career has lurched from bit parts in low-budget films and animations to releasing two albums that were met with disproportionate derision.

“I wouldn’t change a thing about what I’ve done in the past because what may have been bad choices have all led me to this moment,” she says defiantly. “I’m incredibly happy because I’ve got my beautiful baby and lovely partner.”

When I meet her in Glasgow, where she is filming a new BBC drama, The Deep, she seems relaxed and happy. The inner city is a long way from the windswept Malibu property she shares with Henry and their black labrador Bubba, but, Driver, who was born in London, says: “My whole family is in the UK, so it’s been great for Henry to spend time with his cousins. Could I move back? No. I live my life outdoors, surfing, hiking, riding and running along the beach in the sunshine, having barbecues; even though I miss home, I couldn’t do the things I wanted to, personally and professionally.”

It could be argued that some of the things she wants to do professionally might be tricky with a baby in tow, but, luckily, her son seems as much of a pro as his mother.

“Henry was four months old when I started filming with Hilary Swank in sub-zero temperatures in Michigan last February,” Driver says. “Luckily, he was a good sleeper and was feeding on schedule every three hours by then, but I felt so fat and milky and sleep-deprived. It was hilarious watching these massive Michigan teamsters boom in their deep voices across the set, ‘Everything’s gotta stop! Henry’s gotta eat; it’s breast-feeding time’. The cast and crew doted on him.”

Driver credits the parenting guru Rachel Waddilove for helping her to settle Henry into a routine. “There’s no way, as a new mum, I could have let Henry cry for long; a little bit maybe. Besides, once you get your feeding sorted, their sleeping patterns fall into place. I’ve never brought Henry into bed with me, which was very hard, but I wanted to teach him that his bed isn’t a scary, isolated place. Now he’s the happiest, funniest, sweetest and most adaptable baby; he has slept in more drawers, walk-in closets and hotel bathrooms than you can imagine. We’re proper gypsies.”

Driver glows as she talks about Henry’s first words and learning to walk “like a little drunk Frankenstein”. But despite the obvious joy that motherhood has brought her, the actress recently had to deal with the sudden death of her father. “When my dad died in December after a heart attack, just a week into shooting The Deep, it was one of the very worst times of my life, but I’ve never felt so loved and taken care of,” she says. “Burying him two days before Christmas was so hard, but [co-star] Jimmy Nesbitt and the crew rallied round and really helped me get through it.” She wore a red dress to his funeral as a tribute to his sense of humour “because my father always used to tell me that I was the kind of girl who would wear a red dress to a funeral”.

It was acknowledging how important that support was to her, and realising how “motherhood has given me a much broader perspective about what hardship really is” that led Driver to become an ambassador for the 3 Rifles regiment through the sale of Love Bullets, a specially decommissioned bullet set with a Swarovski crystal. The money raised will be used to help the families of dead and injured soldiers.

“Regardless of your feelings about the war in Afghanistan, the lack of moral and physical support given to families of serving personnel, the injured and the bereaved is an insult and embarrassment,” she says. “These are women struggling to hold their families together. The hardship of others really makes you put your own life into perspective.”