As a kid growing up in Texas, Woody Harrelson daydreamed about being a cop and, later, some kind of secret agent – like an American James Bond. “I was probably influenced by stuff I’d watched, thinking how glorious it would be,” he says in that unmistakable, slow, Southern drawl. “But, oh my God, that would have been horrible. Can you imagine me protecting President Trump? I’d pin a fricking target on him.”

Harrelson is laughing, but only half joking all the same when we meet at the Venice film festival. He’s full of laid-back bonhomie, wearing eco-friendly hemp chinos, a white T-shirt and a hipster beard. He’s been foregoing the pleasures of weed for some time now, but he remains, essentially, the most affable of dudes; the most right on of Hollywood’s elite; the walking embodiment, indeed, of all things not Trump.

He returns to the subject when we speak on the phone a few months later. He’s back in Maui, the paradise island he now calls home, explaining why Willie Nelson, his Maui neighbour and friend, would make a better leader than the “narcissist” currently in the White House (and he’s only half joking again).

Trump is exactly what I expected. It’s ‘Let’s make money, let’s deregulate.’ He is a disaster

Just last night, before our phone call, he and the country music legend had been hanging out, the latter trying to entice Woody to share a bong with him. “He was handing it to me and I was like, ‘Goddamn! That smells good!’ But I didn’t.”

Before giving up, he says, he’d blurred the edges of an overly sensitive nature by existing in a perpetual weed-induced fog. “Whether it was a San Francisco fog or a London fog, there was always some level of fog going on. But now I want to get my head together. I want to see things clearly, to be aware and sensitive to what’s going on in my life and in the world, although I admit it’s tough sometimes.”

In a world in which celebrity is now micro-managed by agents and publicists, Harrelson is old school. He rarely takes offence at questions, answers honestly, is slow to big himself up, quick to put himself down, describing himself, for example, as “a pretty lazy guy, at heart”.

“To be honest with you, I could just lie in bed until 1pm and then mosey down and pick a mango or something, then go out with my buddies.” After our phone call, he’s off to the beach to kite surf before meeting his mates for a twice-weekly football kick-about.

Right side of the law: Woody as a small town cop with his director Martin McDonagh on the set of Three Billboards Outside Ebbing, Missouri. Photograph: Merrick Morton/AP

Paradoxically, when you study his rammed CV you find that in the past 18 months alone he’s made seven movies, including the Oscar-tipped Three Billboards Outside Ebbing, Missouri, a Star Wars spin off (Solo: A Star Wars Story) as well as making his directorial debut, with the hilarious, soul-baring Lost in London.

“I kept thinking: ‘I’ll do this one and then I’ll take a break.’ And then another one would come along and I’m greedy for a good role. It’s like Billboards. I’d be a fool to turn that down.”

Written and directed by London playwright Martin McDonagh whose other credits include In Bruges, Three Billboards is a brilliant portrait of life in small-town America with crime, tragedy, black humour and a love story all vying for position.

Harrelson plays an unlikely hero – Bill Willoughby, a police chief who becomes the focus of a local woman’s campaign for justice. Mildred Hayes (Frances McDormand) rents three dilapidated billboards on the road into the redneck town of Ebbing to pose an embarrassing question: why has Willoughby not yet arrested whoever raped and murdered her daughter, Angela?

Star struck: Woody with the cast of Solo: A Star Wars Story. Photograph: Walt Disney Ltd

It won rave reviews and the prize for best screenplay at Venice, has Golden Globe Best Actress and Best Film nominations, and may yet win Oscars for all three of its main stars, McDormand as the grieving, ballsy mother, Sam Rockwell as Willoughby’s dumb, racist sidekick and Harrelson as the man at the moral heart of Ebbing and the film itself. “He’s just a really good guy who’s trying to do the right thing – not just as a cop, but as man who’s trying to be a good father and a good husband to the woman he’s always loved.”

Harrelson has been nominated for Oscars twice before, for his role as the soft porn magnate in The People vs Larry Flynt and the army captain in The Messenger. Yet, he says, he gives, “not a moment’s thought” to whether this might be third time lucky.

“Frances is brilliant and so is Sam, and I know this is a great movie. But most of all, I just hope it does well and that people go and see it because, in the end, that’s why we make movies and what we always hope for.”

Playing a cop seems to tickle Harrelson. In his own life, he admits: “I generally have a weird time with authority – so when I first played a cop I thought: ‘I don’t know if I can do it.’”

He’d been marked by the experience of being arrested at the age of 21 after a drunken night in Cleveland, Ohio.

Love interest: Woody with his wife Laura Louie at the Three Billboards Outside Ebbing, Missouri première, Venice, September 2017. Photograph: Action Press/Rex/Shutterstock

“I jumped out the truck, wearing the cuffs, and ran across the parking lot and there was never going to be a good ending to that,” he says. “But those cops were cruel to me, you know. It sure ended any fascination I’d ever had with being a cop.”

His background, too, was at odds with a career in law enforcement. He was born in Texas, but moved to Ohio with his mother Diane, after his father Charles – a contract killer – was sent to prison for the murder of a grain dealer and later for shooting a federal judge.

He rarely speaks about his father, who died in jail in Colorado in 2007. If you push him to think of any positives, he cites his father’s advice to ‘“always keep an open mind”.

“I think that philosophy has helped me at times to take another look,” he says, “and not shut down to things that I might otherwise have been closed off to.”

Still, it was his mother who taught morals that guide him even now. “I do feel she was a great influence on me and instilled a lot of good values – just the way you treat people, behaving honourably, which I don’t always do, but she was a great role model for that and still is.”

Early days: starring with Ted Danson in Cheers. Photograph: Moviestore/Rex/Shutterstock

Not surprisingly, he admires strong women and fell in love with one. He and Laura Louie, formerly his personal assistant, have been together for 25 years, married for 10. They met when Harrelson was still reeling from the success of his breakthrough role as barman, Woody Boyd in Cheers – a role he played for eight years. Before he’d been a struggling actor who’d moved to New York in search of stage roles after graduating from Hanover College, Indiana, where he studied English and Theatre. He found sudden fame hard to deal with.

“Before, I’d been gregarious – someone who enjoyed the company of others. But during Cheers, the pressure of people that I didn’t know constantly wanting to talk to me made me recoil and become less outgoing. It had quite a negative impact. I went through a period of arrogance and having my head up my ass,” he admits. “But, luckily, this life and my family – my wife and my daughters [Deni, 24, Zoe, 21 and Makani, 11] they kind of loved me into a better human being.”

For all that, he could easily have lost Laura. He turned a particularly lurid time in 2002 into a film, Lost in London, which shows “the worst night of my life”. It was shot in a continuous 99-minute take on the streets of the capital and streamed live to cinemas in the UK and USA last January. It shows a foursome with women he’d met in a bar, damaging a taxi and another night in the cells, events that were all splashed over the tabloids – when he was in the UK appearing on stage in On An Average Day.

“You know, that was a tough time and the film was cathartic for me and for Laura, too, because, in a way, it’s a kind of weird love letter to her.”

Dark side: with Matthew McConaughey in True Detective

As to the various sex scandals now engulfing not just his industry, but also the world of politics and media, Harrelson is philosophical.

“When this all started up, a guy like Harvey Weinstein wasn’t much of a surprise. He’d always seemed like a real weird, lecherous guy, but I knew, eventually, it would hit politics, too, and sure enough it’s happening. But, then, there are going to be predators across every profession. And, in a way, what’s happening is great because, hopefully, the more people that come forward, the more people that deserve that kind of attention are weeded out.”

Now 56, Harrelson’s measured worldview is matched by a maturity in his work. Harrelson has delivered some of his best work in recent years – playing a troubled cop on the trail of a serial killer in the HBO series True Detective, a vulgar yet endearing career politician in the underrated LBJ and lending credibility to big franchises like The Hunger Games and now Solo: A Star Wars Story which was filmed in London.

Before joining the cast as Garris Shrike, a mentor to Han Solo, the Star Wars juggernaut had mostly passed him by. “I liked the movies, without being a fanatic,” he says. “But to be offered that role felt like a very cool opportunity.”

‘The worst night of my life’: Woody dodges traffic in Lost in London

What he hadn’t realised was the level of secrecy involved. “You don’t even get a script,” he laughs, “It’s all done on an e-reader with an encrypted password and if you so much as walk off set, you have to wear a cloak in case a drone flies over and takes a picture. It’s crazy.”

I’m a pretty lazy guy. I could lie in bed, then mosey down and pick a mango or something

Harrelson sees benefits in these troubled times of escapist, upbeat movies like Star Wars. They are, perhaps, one of the antidotes to the looming presence of Trump in the White House.

He met the president once, when his friend, Jesse Ventura, was governor of Minnesota and Trump was hoping he’d become his running mate, on the Democrat ticket, in the 2004 election.

“We went over to Trump Tower – talk about a tough dinner to get through. All he could talk about was money. After about 45 minutes, I was like ‘excuse me’, and walked outside and fired up a joint. I was like: ‘Whoa, how am I going to get through the rest of this meal?’ I wouldn’t even have dinner with that mother and here he is the fucking president.”

A committed environmentalist – he once climbed the Golden Gate Bridge in San Francisco to unfurl a banner protesting at the felling of giant redwood trees – he’s pessimistic about the future.

Oscar nominee: Woody in The People vs Larry Flynt. Photograph: Columbia Pictures/Sportsphoto/Allstar

“Trump’s pulling out of the Paris Accord and he’s opening up all kinds of wilderness areas and parks to the extractive industries. He’s exactly what I expected – he’s a businessman making deals with other businessmen. It’s ‘Let’s make money, let’s deregulate.’ A lot of these regulations were very hard to pass in the first place, because of the power of these industries, and now he has taken what little regulation there was and is destroying it. Ecologically, he is the biggest disaster ever to happen.”

In the past, Harrelson has withheld taxes when he disagreed with government. “But, really, I don’t see how it helps. Yes, I do feel the need to be active and doing something counter to the bullshit going on, but then I’ve fought before and never won and the whole thing has cost me a fortune.”

He may not be about to revive dreams of a career in law enforcement, but his focus on politcs is clear. The wild days of Woody are definitely over. “There’s that saying that the road of excess leads to the palace of wisdom,” he grins. “And if that’s true, then I must be extremely wise.”

Three Billboards Outside Ebbing, Missouri opens in the UK on 12 January