There are a lot of gossips who like to think that I’m a snogger, but I’m pretty prudish,” says Kate Hudson. “I need to find that 18-year-old in me again, who was way more adventurous when it came to kissing boys. I’m not really like that any more.”

It’s February, and Kate, 28, is in London to promote Fool’s Gold, a flirty diving movie in which she stars opposite Matthew McConaughey’s pectorals (Kate’s tomboyish derring-do proving a good foil for McConaughey’s wild-man antics). Wearing a cobalt-blue Burberry frock, her cute new fringe blown straight and a date with best gal pal Stella McCartney on her dance card for the evening, she is clearly in an up-for-it party mood when she professes an appreciation of the allure of the British male: “Are you kidding? Oh, yeah – I was just having a discussion with somebody about that boy in Control [Sam Riley]. He’s very cute.” Just don’t expect to see her stumbling out of a cab in the wee small hours with a palefaced indie buck lassoed to her handbag. “I would love nothing more than to have a good, honest make-out sesh,” she admits with winning candour, “but I find it really hard, because I’m a mom, and I have no interest in being someone who is out, acting at all like that.”

For a girl who nimbly surfs Hollywood’s frothy waters, Kate prefers to style herself as a feet-on-the-ground single mum. Perhaps we should remember her DNA – her mum, Goldie Hawn, is the sort of offbeat lioness who combines a wildly successful screen career as the high priestess of knowing ditz with wholesome, hands-on child-rearing in Colorado and an impressively robust relationship with her long-term lover, Kurt Russell. “It’s their silver anniversary,” Kate announces proudly. “Twenty-five years of not being married. It works. They go through their stuff just like everybody else, but they are so happy. A wedding never made it any better or worse. It’s awesome.”

Kate’s own marriage to the Black Crowes front man, Chris Robinson, father of her four-year-old son, Ryder, ended in 2006. The pair remain on excellent terms. “I spent 7½ years with Chris. I grew up with him,” she says. “It takes a grown-up to be able to realise that something’s not working. The transition with children is when you get scared. It’s a huge decision. Well, I still love [Ryder’s] dad. It’s that simple. Daddy and I still spend lots of time together.”

In fact, she seems so sane on the subject of break-ups, co-parenting and trying not to let your own ego get in the way of your child’s happiness, I suggest she might write a manual for Hollywood’s single mums (cue much head-shaking and self-deprecating laughter). Does she ever feel restricted by having a child? “Well, I am restricted. The question is, does it bother me? And it doesn’t at all. I’m a mom and that’s my first priority. There are a lot of people who say, ‘Do you know what I did for you? Have you any idea about the things I gave up?’ I could never be like that. I can’t wait to have more. I’m at that place when I’m ready to have another one and Chris and I are not together. I’m like, ‘Oh no! Uh-oh! I’m ready.’ ” As for dating as a single mum: “Any guy I ever meet is always going to come second to my son,” she says. “And you get to weed out the boys from the men. You definitely know which ones are the boys.”

Which leads us on to the hot topic of Kate’s recent reunion with her on-again, off-again love interest, Owen Wilson, snapped together once more in Miami on a demure family-style cycling trip, complete with little Ryder sensibly wearing a helmet. Her romance with Wilson – they met on the set of the 2006 comedy You, Me and Dupree – has been far from straightforward.

When I first interviewed Kate in her Los Angeles home in May last year, their relationship had just ended. Wilson’s subsequent suicide attempt last August was clearly devastating; it was reported to Kate when she was on set filming her next movie, My Best Friend’s Girl. Not that she will be drawn on it – much. “I’ll tell you what I have learnt this past year. Some things are better left undiscussed,” she says flatly. “It doesn’t help anything. It’s better left for me and the other people involved.”

When I ask her about the other chilling event of recent months that touched her life, the tragic death of Heath Ledger, with whom she starred in the period drama The Four Feathers, she is uncharacteristically lost for words. “It was shocking for everybody.” She pauses. “He was a lovely person and it’s just tremendously sad.”

Reticence is not really in the nature of plain-speaking Kate, who has always managed to walk the tricky line of being a Hollywood-dwelling everygirl. Nevertheless, the past couple of years spent shadow-boxing the tabloids have taken their toll. “It’s like being in high school and not asking for it,” she says, shrugging wearily. “I really believe you have to protect your joyfulness.”

And what a lot of joyful happenings she has in the pipeline. Having just signed up Ryder for football and Tee Ball (a baseball-type sport for youngsters) classes, she is wildly enthused about his sporting future. “I love sports,” she says. “I know more about them than my brothers sometimes. I’ve never been more excited to be a soccer mom. And I will totally be the snack mom – that’s going to be the best part.”

Nor could she be happier about her friend and co-star McConaughey’s impending baby bundle, although she’s not likely to start ladling out advice. “He’s going to be a great dad,” she says. “Everyone has an image of Matthew, like he’s the shirtless wonder, climbing mountains and kind of crazy, but in fact he’s very devoted and quite responsible.”

As for coming movie attractions, she is producing her first feature, Bride Wars – a kind of bridezilla face-off with, she promises, some darkly sexy undertones – in which she will star alongside Anne Hathaway. The pair have already bonded like glue and are in cahoots about casting their male co-stars. “My girlfriends are so important. They have got me through so much in my life,” Kate says.

The girlfriend principle is another thing she has inherited from her redoubtable mother. She has a story along these lines from her sister-in-law’s wedding shower: “My mom is like, ‘Everybody look around the room. You guys all love each other, every single one. But remember this. Your life is nothing without every person in this room, because men come and go, and the women are always there.’ ” Kate brushes down her skirt and starts to gather her things for the evening ahead. “Women are always there for each other.”

Fool’s Gold opens on Friday

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