The experience of playing an end-of-life healthcare worker did not alter Tim Roth’s feelings on legalised suicide, the actor has said in Cannes.

“I’m all for it. Absolutely. But it’s such a complicated subject for some of governments.”

That assisted suicide is still illegal in the UK, said the Los Angeles-based Roth, is “crazy”. But the actor said the more research into the field he’d done, the more evident it was that the law was far from watertight.

“When you go about asking people in the know how to do it [you learn] it happens all the time.”

Roth’s director, Michel Franco, agreed. “Nurses do it more often than people realise. There are big debates about whether it should be legal or not. I agree with Tim – of course it should be legal, and done in a proper way. But it also happens all the time.”

Chronic is the penultimate competition film to screen at this year’s festival, with just the Michael Fassbender-starring Macbeth still to come. It met with an impressed if muted reaction at the morning press screening – Franco’s fourth feature is the strikingly bleak story of an end-of-life nurse struggling with his own personal trauma. Roth’s character, David, tends to a number of patients to whom he becomes close - for some of their relatives, too close.

Playing the role, said Roth, was “very disturbing”. As research he trained with three nurses and admitted that “as someone who’s not yet ill I find aspects of their behaviour annoying”. He could also appreciate the jealousies which can arise in such a situation, he said. “They’re having a relationship with the patient the family can never have.”

Said Franco: “I wanted to make an objective portrayal of how complicated those moments of life are. And how a stranger lives through that and gets involved in personal matters.”

The film was inspired by the death of Franco’s grandmother, who was bed-bound in the months before she died, and tended to by a veteran palliative nurse in whom the director became interested.

“I was very moved and intrigued by the idea of the life of someone who deals with illness as a permanent.” When he asked how many deaths she’d witnessed, Franco recalled that the nurse simply “smiled very sadly”.

Franco and Roth first met at Cannes in 2012, when the actor was chair of the Un Certain Regard jury who awarded Franco’s After Lucia their top prize. Although the bulk of Chronic was shot in America, working with the crew for a while in their native Mexico was eye-opening, said Roth. “It’s crazy the stuff they get away with. Unbelievable! Really dangerous.”