Everything comes from reality. The brutal, graphic violence in the movie came from our research. The suicide at the opening of the movie is not in the novel, but when we were talking to real inmates and guards at the jail they told us the story about an inmate who was complaining he had a headache all the time.

The doctor diagnosed him through the bars of the cell and told him it was diarrhoea. Finally the guy committed suicide and the results of the autopsy showed that he had a tumour the size of a kiwi fruit.

This was reality. When we were writing the script we thought that it was a very hard, direct way to open the movie. This is what the film is, if you can stand it, suffer it, then okay otherwise you still have time to leave.

But to my surprise and my happiness the movie affects every type of audience. Even old ladies have come to me and said this is a very beautiful movie, they say it’s violent but it is not gratuitous.

- Can you tell us something about the casting?

This is an ensemble movie, so for me it was absolutely important to get the best actor for each character role. It was Kubrick who said that the best a director can do with his actors is to choose them well.

It’s so true, I spent eight months auditioning and trying to get to know the actors in preparation for their roles. The most difficult part to cast was Juan. We made hundreds of auditions and I could not find an actor to play Juan because it is a really difficult role. He’s a normal, friendly guy at first who is going to change totally, who transforms into a dark and haunted soul by the end of the film.

I realised in order to find one guy who would be believable with this transformation I needed to cast an unknown actor.

But it was very difficult because he had to be able to confront an actor like Luis Tosar who plays Malamadre, and convince him of his disguise. Finally my casting director remembered 'that one guy, who won an acting prize in a contest of fighting, take a look'.

When I saw Alberto Ammann I felt something about his size, the strength of his look, everything. His image was a really great contrast with Luis. With his clean cut features so pure, so innocent, Alberto made Luis seem even more brutal.

So we made an audition between them and it was great, They listened to each other, they looked at each other, they were alive, feeding off each other and I was convinced that this was the correct guy to take on Luis’s Malamadre.

Cell 211 is out 9th January.