Q: This is supposed to be an unfilmable book - what were your fears going into it?

A: The biggest thing was that it was a sacred text, Gabriel Garcia Marquez is a great sacred elephant of a writer.

People who cannot possibly have known him call him by his diminutive Christian name - he's known as 'Gabo' - so there's a kind of possessiveness which is very daunting.

I was scared of that, probably with good cause. Beyond that this is a great, great book. I can be as snippy as I like about people thinking that they own it because I think I own it. It is a great book, and of course a movie can only ever be partial. For which I'm truly sorry, there are still scenes that it kills me not to have.

There's the most wonderful first chapter, which everybody said I'd be dumping, and I looked at it and thought maybe not. It's a character that you get to know very well as a young man and stays with the story. One of the glories of the book is that it's whole lives, writers don't write whole lives.

This is a story about a person who begins at 17 and ends at 77. So you might the third of the great long running characters in the movie on the day of his death when he's in fact gone to sign a death certificate on a friend of his who's committed suicide.

They say, "what are you going to put as cause of death?", and he says "I'm going to put gerontophobia" meaning the fear of old age. That's the word he uses. This man had said publicly that he didn't care to survive beyond 60 and the whole story is encapsulated there in a sense, it's what happens to people when they get beyond the romantic phase, when their bodies are no good any more, when their teeth fall out and they have arthritis.

It's what happens to life and the great life giving emotions as you get older. One of the things that I absolutely loved about the book is that it's uncompromisingly about old people as much as anything else. You follow these lives through until they're old, old people and they make love to one another too. That sense of wholeness I thought was fantastic in the novel and that's the thing that made me want to do it.

Q: Didn't the book's author Gabriel Garcia Marquez give you licence to adapt it freely?

A: Well he did, but he's a difficult chap to pin down. One of the things he said to the writer was "you're being much too respectful to the text". Then when he first saw the movie he liked it. Six months he changed his mind, the old bugger. And I don't mind calling him that because I think he is. He said "wonderful work, congratulations, and now with all the stuff you've left out we can make the second movie".

In other words he encourages you on the one hand and on the other he regards it as a sacred text himself. Or you could do better. Or why did you put that bit in and take that bit out? Or any of those writing choices. It's very, very, very difficult.

Q: Were you ever tempted to make it in Spanish?

A: No I wasn't. I have always loved the movies of Julian Schnabel, I adored Basquiat and I loved Before Night Falls and loved The Diving Bell & The Butterfly. One of the things I saw in Before Night Falls was that he had this colossal polyglot cast, they came from all over, Johnny Depp was even in it.

No two people seemed to be the same nationality, he had simply cast for the qualities of the character and actor. And then he stuck it all together by giving them all a very closely observed and worked Cuban-English accent. I didn't feel able to do this in Spanish because I don't speak Spanish well enough.

If it had been in French I would have given it a go, because I probably could have got through that. I tried to learn a little basic Spanish for the film, but I wouldn't have any of the sense of what the manipulation of the language would have been.

I would do the same trick as Schnabel had done with the Cuban movie. That would also free me, by the way, to go anywhere in the Latin world which I enthusiastically did. I hunted the best actors. I went to Brazil and got Fernanda Montenegro. I went to Mexico, to Spain and to Italy. I tried to stay inside the sensibility but not necessarily inside the language.

Q: The last major film you directed was Harry Potter and the Goblet of Fire

A: I was very much wanting to clean my system out, to do something completely other. An antidote, you know? Because the Potter films have a very strong identity, they are difficult, they're very, very long and they take absolutely everything that you've got and more.

So I wanted to do something as far from that as I could, I wanted to do something that was triumphantly human and not comically magical. And so there we are, it was a great book. Plus I simply loved what it said, that at the end of this story which is full of distress and comedy and obsession and so forth, that could at any turn when you look at the film could turn bad.

"Look what he does, he does terrible things. He kills somebody, that girl who has her throat cut. And at the end of that his whole life has been run by this obsession he can actually say - and it's a direct quote from the book - that, to his joy, he discovers that it's life and not death that is the great motivator of people. And that sort of humane-ness is very rare these days, it just doesn't happen.

Q: Are such complexities one reason why the book was deemed unfilmable?

A: Yes, I think that is partly it. When you're still shaping the film you take it out and screen it to test audiences and these people, it was in California, but there were some very vocal English people there and boy do they talk.

They felt very strongly that it was unfilmable as it currently stood because we didn't have enough magic realism in it, talking about it as if one would simply go to the magic realism shop and buy a couple of cartons and pour them in. Stir vigorously and drink.

I think that there is a kind of eccentricity and particularity in the writing, but I don't think that this is a book that is full of the kind of classic magic realism the way for instance Hundred Years of Solitude is, where blood does run up hill.

Where things that are clearly impossible happen. There's a wonderful Scots word, "pawki", a sort of sneaky, ironic look at how people are and what their ambitions for themselves are. There's much more of that in this book than there is direct heroic magic realism.

Q: Does Hollywood prefers black and white morality?

A: It does, of course, and that's partly why it's regarded as unfilmable but I think it's also it's regarded as unfilmable because people feel so possessive of it and therefore only the individual's imagination is the lens through which it should be seen. So your version of the read is not my version of the read but it's more important than mine, and so on.

I think it's a book that uniquely needs to be possessed by the people who read it. But I think movies should be a broad church and should introduce an audience who maybe had not read the book but now might go back and read the book. And then you might say well the movie didn't get it right at all, but boy what a book it is'.

That's fine by me, that's a good result for me. I think that exclusivity, I don't think that Marques' humaneness asks for that kind of exclusivity either.

Q: How was your star Javier Bardem?

A: He is a great actor, absolutely, by virtue of how completely he delivers himself to the character. And of course he could read the novel in Spanish so he knew there were linguistic tricks that the novel plays.

Javier, to my frustration, could have all sorts of responses to the novel that I couldn't. He would try and explain to me but it's very difficult to grasp in a language which he doesn't have. His English is very good, he can act in English, I think he can probably act in any language. He has this extraordinary ability to zero on something.

He is so zeroed on the emotions that he has, that the character has. He's living in the interior world of his character.

The only other time I've seen it was with Al Pacino where if I didn't shout "cut!" on Donnie Brasco he would ramble off into the murk of Queens and never be seen again. He'd stay in character until somebody said "cut!" at which point he'd wake up - perhaps after years, having been his character all the intervening time. Javier's like that too.

He ages fantastically. Physically he's wrong for the role, the role is supposed to be a small, ratty, not particularly attractive person who is extraordinary by virtue of which the intensity with which their flame burns. Whereas Javier is a great big rugby player.

But he's such an actor that he gets the character in the head and that then translates into the body somehow, somewhere along the way. The ageing process with him was fantastic, watching him inch it forward because there aren't great big jumps in it. He has to play a couple of years at a time.

You can't make any grand operatic effects, you have to grind through the process of the muscles getting weaker and the joints getting stiffer. The judgement and the ability that he brought to that, I used to love watching him do the ageing.

Love in the Time of Cholera is in cinemas from Friday March 21.