He seems to have been born without the ability to feel embarrassed about himself. He speaks without any kind of filtering process, from his core. He gives you wincing minutiae. Ioan Gruffudd doesn’t tell me what he thinks I want to hear. He doesn’t manipulate. He doesn’t even expect me to have watched his performance of Tony Blair in Oliver Stone’s W. He hasn’t seen it himself, the process in the cutting room having been so long and fractious. He doesn’t need a film to plug to allow an interview like most Hollywood actors.

He wanted to make sure we meet before I left Los Angeles. So here we are on the patio of the Four Seasons, garden umbrellas beating off the baking sun. Gruffudd is wearing dark jeans and a washed-in grey T-shirt. It clings and hangs in all the right places. His jaw is chiselled, his hair is dark-brown curls. Around his neck a silver chain on which hangs a gold wedding ring. He is extremely polite; to me, to the waiters, probably to everybody.

He has lived in LA since 2003 and he unashamedly loves it. “Which is an easy thing to admit in America because that’s the way they are brought up, to be successful and ambitious. It’s the American way. The British are incredibly ambitious and driven, but you’re not allowed to admit it. Such horrible false modesty drove me mad, actually. I don’t miss London at all.”

Indeed, he and his former flatmate Matthew Rhys form an integral part of the LA Taffia. Rhys is in the series Brothers and Sisters, with Calista Flockhart. They play football with Tom Jones on Robbie Williams’s converted tennis court. Ioan Gruffudd (pronounced You-an Griffiths) has a tea towel with the Welsh flag on it that he would take to every hotel and set. He loves all Welsh things, but he’d rather be a Welshman in LA.

Welsh is his first language and his father was the well-loved headmaster of the school he went to in Cardiff. He was a diligent oboe-playing student who lucked out when he was cast in the Welsh soap Pobol y Cwm (People of the Valley), aged 13. He went to Rada, remained unnoticed until he wore some breeches and ruffles to perform in front of agents. His curls and broody eyes made him look romantic and heroic in equal parts. He was snapped up for the remake of Poldark. Then he was Horatio Hornblower in the ITV1 nautical drama for six years from 1998. His first screen kiss was with Stephen Fry in Wilde. He was the lead in 102 Dalmatians, where he met his wife, Alice Evans. He was in Black Hawk Down, and played Lancelot in King Arthur. His most lucrative deal has been as Mr Fantastic in Fantastic Four, but as William Wilberforce in Amazing Grace he showed he had the charisma, depth and heart to carry a film. Wilberforce fought for the abolition of slavery. He was vulnerable, strong, innocent, emotional. Perhaps the closest to Gruffudd himself.

We order matching cappuccinos and tap water and he tells me how he was late to rebel. “It sounds boring, but I enjoyed school. I didn’t resent the fact that my father was the headmaster and I didn’t feel the need to rebel. It wasn’t until I was at Rada that I started to enjoy drinking.

But I didn’t have any great need to experiment or dabble in anything. The way I was raised made me aware of the dangers of that sort of thing. But also I’m a very contented person – that’s something I was born with, it’s a blessing really.” Curiously, the readiness with which he admits to being boring makes him fascinating.

He also seems to have been born without cynicism, or an ability to dislike directors that are well-known tyrants. He met Oliver Stone at a party. “Josh Brolin was at the same party and we sat next to each other having a good laugh. Oliver Stone came over and claimed to have seen me in a film playing an agent, although I don’t remember that movie. Anyway, he said, ‘Nice to meet you both, look forward to working with you one day,’ and a few months later Josh gets offered Bush and I get offered Blair.

“I think Oliver has calmed down. I heard in the past he was a tough cookie, but he was charming with me – very fatherly. He wanted me to understand the political connotations of everything I was doing. He would take me to one side and put his arm around me. He’s incredibly mellow, a real humanitarian.”

He tells me that he received a phone call from Stone apologising that much of his part had been cut. Gruffudd doesn’t seem hurt; he presents this as an act of chivalry on Stone’s part. I tell him that I found Stone angry and bruised when I met him. “I think he’s changed a lot. At the audition he kept asking me, ‘What do you think the British press will think of you playing Blair?’

He was concerned, testing me a little bit.

“It was Blair just before the war, so he was about 50. I wanted to present a Blair that people could instantly recognise, so I worked from the outside in, as we say as actors, instead of finding the character and bringing it out. What were his mannerisms? What did he look like? I think Oliver was trying to present W as someone who lived in the shadow of his father, a bright and successful president when his son was a bad boy. He found God as his saviour and therefore his life turned around. Everything was conditioned by his beliefs and that’s what we were trying to touch upon in the movie. God was how Blair and Bush bonded.”

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