There are worse jobs than being a movie star. Still, you don’t envy them the sprawling press junkets that require the talent to spring miniature variations on the same story to 100 journalists. No wonder they so often seem faintly sedated.

Paula Patton is something else. In Knightsbridge to flog her performance as a pistachio-coloured ogre in Duncan Jones's Warcraft, she positively fizzes with energy. And she's so nice. She remembers your name. She asks questions back. Manners cost nothing, you know.

“Well, I do enjoy it, Donald,” she says. “I am grateful to be able to do it. You flew from Dublin? Oh, I love Ireland. I was there just over a year ago. Sit on the couch with me! Come on.”

That sort of thing.

It's not as if she won't be juggling tricky personal questions. Patton has been a familiar face since she secured a leading role opposite Will Smith in Hitch 12 years ago. She was very good in Precious. She kicked the proverbial ass in Mission: Impossible Ghost Protocol. But she will find it hard to avoid queries about her 23-year relationship with lounge-pop sensation Robin Thicke.

They first began dating in 1993. They married 12 years later and divorced in 2015. That’s a long, long time in this business.

“Yes, it was a long time, but obviously it didn’t work out in the end,” Patton says wistfully. “But there’s a time for everything in our life. There is a moment when society will tell you what is right or wrong, but you have to trust something inside your soul. If you aren’t happy wherever you are, then nobody should force you to stay there.”

It's been a peculiar sort of break-up. The word "amicable" was bandied about, but Thicke did – at about the time the divorce was being finalised – release an LP called Paula and a single titled Get Her Back. Thus are relationships publicly played out in the modern world.

Live to the max

“I would have loved the idea of my son having two parents together,” she says, positivity undimmed. “But I made this decision and I encourage men and women to be honest with themselves. We only have this one life to live and you do have to live it to the max.

“You have to do the things you’re meant to do. Sometimes the thing you’re most afraid of is the thing you’re meant to do. Fear is a liar.”

I get the impression we could draw inspirational conclusions from her break-up for the rest of the day, but there is a career to be discussed. Patton (40) was born in Los Angeles, with a teacher for a mother and a lawyer for a father. It sounds as if she was a bit of an academic star, attending first Berkeley and then the film school at USC. Those are serious universities.

I wonder what persuaded Patton to move from behind the camera and become and actor.

"Ever since I was a little girl, I loved to act," she says. "I would put on plays in my parents backyard. My favourite game was make-believe. Escaping my realty as a little girl was important. I ended up going to a performing arts high school. Like in Fame."

She makes the younger Paula sound close to insufferable.

“Ha, ha! That’s funny. I got interested in film-making. I went to USC. I did the PA work you have to do. I did some documentary work and then I just had this moment where I went: Aha! What have I wanted to do since I was a little girl? Be an actor.”

Paula’s father is black and her mother is white. Ten years ago, when she began to get top-flight work, the conversations concerning race and Hollywood were already heated. Since then, however, the temperature has raised significantly.

Expected exotic

Patton's character in Warcraft – half-human, half-orc – is the sort of "exotic" role that the industry always put the way of African- American performers. It is more significant that she secure parts such as that in the Mission: Impossible flick: a role that would, a few years previously, have automatically gone to a white actor.

Is the situation improving?

“It has got better, I think, from when I was in high school. We have a long way to go and it can be very frustrating. I want to believe that people often don’t know any better and their minds just have to be opened.

“Will Ferrell did this stand-up where he’s president Bush and he says: ‘People say I hate black people. That’s not true. I never ever think of them. They never cross my mind, so how could I hate them?’ That’s the issue. Let it cross your mind. Things are changing. It’s happening.”

And yet. A spectre is looming across the land. The spectre is Donald Trump. An endlessly positive person with apparently unquenchable energy, Patton can’t be happy about the Queens orang-utan’s apparently unstoppable advance on the Republican nomination.

Trump is sort of the anti-Patton: a belligerent manifestation of atavistic rage. Sure enough, her face sags a little and she sighs in uncharacteristically melancholic fashion. A light has been dimmed.

“It’s a really upsetting thing to think that a person who lacks any kindness or compassion – who’s so immovably stubborn – could become the leader of so many people,” she says. “It’s embarrassing that so much of American culture has embraced him. I can only hope that the way the media tells the story is not the reality and that the people will speak and that’s not going to be our future.”

The mysteries of the Trump story are hard to unravel for the political liberal adrift in the entertainment industry. You could spend a month in southern California and never meet anybody who intends to vote for Trump. We live such sheltered lives.

“Yeah, yeah,” Patton says, “You can drive down a street and never meet anybody who supports him. Here’s the question. How can we move the needle closer to kindness and compassion? What is it that’s happening? Again, it’s fear that makes you want to follow something so dark and evil.”

There are, I suppose, musings on these matters in Warcraft. Jones's incredibly loud, incredibly expensive adaptation of the titular role-playing videogame franchise has much to do with a war between big angry orcs and only marginally less aggressive humans. Patton's Garona is a sort of bridge between the two. Her presence points towards a more peaceful future. I think.

Loincloth clad

“When I was asked to play the role, I was at first super-excited and then incredibly nervous,” she says. “How do I play half-orc, half-human? They have these contact lenses that obscure my vision. My peripheral vision was off. So, I couldn’t see out the sides. Then there’s all the make-up. I began the film in my loincloth. Tusks in my mouth. All that made me feel like Garona.”

And they didn’t actually paint her green?

“No, the technology is moving so fast. They did that in post-production. That way they can see your pores. If you’re hot it reads on your face . . . ”

The alarm in the hotel room suddenly bursts into screeching life. We can here fussing the next room.

“That’s Donald Trump!” Paula cackles. “He’s heard us. Ha ha ha!”