You seem to be working non-stop at the moment...
Well it started at the beginning of last year when I did a play which lasted eight weeks. That was great, I loved that. I then went on to 'Macbeth' [a contemporary TV version]. 'Macbeth' was a f**king nightmare because we had no time to shoot it and it was just ridiculously scheduled. Then came 'The Last King of Scotland'. It was a huge culture shock. It was incredibly taxing. I was in every single scene and it was 14-hour days and six-day weeks and it was just relentless. It wasn't an easy script. I was f**ked by the end of it.

In 'The Last King of Scotland' you play Idi Amin's doctor. What is your character like?
The Nicholas I play is a fairly run-of-the-mill character to begin with. He might have delusions of grandeur, but he is just a normal student who has just graduated in medicine. He is only a GP. He hasn't specialised in anything exciting and sees his life ahead of him and thinks, 'F**k, you know?' His vanity tells him... there is a much greater destiny waiting for him. And it turns out the first thing that appeals to him is to go and help in the Third World.

What is the film about?
The film is about Idi and the film is about Uganda. But one aspect is 'a white guy in Africa'. He [Nicholas] comes in, and thinks he's Scottish and not British, and not part of the colonial problem. Things can be very easy for ex-pats in places like Uganda. It becomes very easy for him when his ego is massaged by the country. He gets a leg-up because of the colour of his skin. He is confident and he has a chance encounter with Idi Amin. That is his story. A kind of an abuse of a country and not knowing he is doing it. And once he realises he is doing it, it is a matter of life and death. He is selfish and vain and arrogant and he should be shot.

Was it tough filming in Africa?
It was really, really different. I mean, Uganda is a relatively stable country. It has its problems. There is still weird ex-pat wealth alongside poverty. The main roads are nice but just look down a side road and it's an open sewer and there are kids playing in it. It is a real two-sided coin. The people in Uganda and Kampala are so lovely. People don't like to raise their voices too much. The weird thing is men and women don't show affection in public but men do. Quite often you see man holding hands walking down the street. Straight men flirt with straight men.

How did you find working with Hollywood star Forest Whittaker?
With this role [as Idi Amin] he descended into some kind of other place. And it was tense. There wasn't a lot of fun to be had when Forest was around because he was so focussed on it. And there wasn't a lot of fun to be had anyway because it was a male-orientated environment.

Did you get on with each other?
Sometimes you get a sort of gallows humour. And because Forest was so deeply in character you don't want to go, 'So how's the wife?' because it isn't going to help him. And clearly I'm not going to treat him as Amin because that is ridiculous. So how do we get on? We talked shop all the time and that is what got me through. But it created a lot of tension... that translates onto the screen.

Do you get taken over by your characters?
Not all of the time. I have done in other roles. But I think sometimes with method acting you can be quite self-obsessed and only worried about what your character thinks. To Forest's credit he was always about collaboration and telling the story through the relationships. And a lot of actors don't, in my experience. They just do their thing. This character is my age, is from the same part of Scotland as me and has my education. It's just about being honest with myself that I'm not a million miles away from this prick.

Are you a bit of a film buff?
I love film, and I love watching films. I don't try and study them. I think the minute you start studying them, you become an industry member dissecting them rather than enjoying them. So if I learn anything from the performances I admire it is kind of from osmosis. I had two years of classical training. We got taught every different method under the sun. You build your own process. And I like knowing that I am actually drawing upon myself, rather than trying to emulate everyone else.

What have you seen recently?
The last DVD I watched was 'Downfall', which I have been meaning to watch for f**king ages. And 'Bottle Rocket', which is Owen Wilson and Luke Wilson and Wes Anderson. I have been consciously carrying it around for a year in my rucksack, thinking I will get to see it at some point. But I really enjoyed 'Downfall'.

'The Last King of Scotland' is released in the UK on 12 January 2007.