The actor, 41, on cowboy boots, childbearing, self-sufficiency and being bullied at school for not swearing

When I started acting I knew nothing. It was a momentous decision to pick up the flyer for the Trainspotting audition. “Destined” is a bit of a poncy word for it, but I do think I was headed in that direction.

Swearing never came naturally to me. I got bullied in school for it. I was pinned up against the girls’ cloakroom wall while everyone chanted at me to swear. All I could come up with was “bloody”.

What looks good on a Texan film set doesn’t look good on Sauchiehall Street in Glasgow. I spent pretty much all my wages from No Country For Old Men on a pair of cowboy boots. They’re ridiculous. It’s like wearing two Christmas trees on my legs.

Watching films I’m in is always odd. It’s hard not to see my faults

I’ve never fought for anything in my life. The story that I had to fight my agent to be considered for a part in No Country For Old Men is bullshit. I just audition for parts and get them or I don’t. I’m not champing at the bit.

Watching films I’m in is always a bit odd, especially when I’m watching them for the first time with other people. It’s hard not to see my faults.

On-screen birth is laborious. I’ve had two babies in real life, and loads on screen. I had twins in some silly film that wanted to be The Girl in the Pearl Earring. It was more like The Girl in the Blue Shellsuit. But I was worried about having to do it again recently. It’s as if I have to prove myself.

I don’t know if my boys [Freddie, 9, and Theo, 4] like any films I’ve done. I took them to the Swallows and Amazons premiere in the Lake District last year. Theo didn’t understand what was happening. Whenever I was holding the baby in the film, he kept shouting: “Who’s that baby?” Then: “Where am I?” He was freaked out by the whole thing.

Everybody was super fit and healthy on T2 Trainspotting, which is remarkable, considering. Jonny [Lee Miller] and Ewan [McGregor] were running up Arthur’s Seat in Edinburgh almost daily during filming. It was very different from making the first one. Never mind hangovers on set, people were still drunk.

I’ve always been pretty self-sufficient. I never had to borrow money from my mum, even in the early days.

Boardwalk Empire was a total leap in the dark. It worked out quite well – five years is a nice amount of time. But I was in an American/HBO bubble for a wee while and I wasn’t plugged in to what was happening back here.

Because of my Celtic brogue, I do get cast as “staff” quite often. But I span the decades. I’m not always in a corset, you know.

Kelly Macdonald stars in the TV drama The Child In Time, on 24 September at 9pm on BBC1, and in Goodbye Christopher Robin, in cinemas nationwide from 29 September