By Darren Waters
BBC News entertainment reporter in Cannes
Andrea Arnold won an Oscar for the short film Wasp in 2005
The British director of CCTV movie Red Road has said the future of 24-hour surveillance of society needs to be debated.
Andrea Arnold is in Cannes with her first feature film, which is in competition for the Palme d'Or.
The film focuses on a Glasgow council official who monitors the city's CCTV network helping to crack down on crime.
Arnold said: "You can see why it is there but we should consider what it means for our future."
The depiction of a city under almost constant and blanket surveillance surprised some non-British film critics and shocked others.
Britain reportedly has 4.2 million cameras, 20% of the world's CCTV, and one camera for every 14 people.
At a press conference for the film one reporter asked if the "Orwellian" depiction of a city under constant watch was real or not.
Cast members of the film admitted they had changed their behaviour since making the film, which cost £1.2m and was funded by lottery money and BBC Films.
"It's unsettling," said lead actress Kate Dickie, whose character monitors the CCTV cameras.
"I used to find it creepy. But having spent time in a centre with the people who do the monitoring and see how much they care, and how much they help people, I am torn."
Arnold said: "There are cameras in big cities, in my local park where there are kids playing and the teenagers will go there at night and kiss.
"So I tell the teenagers not to go there because it's not a good place to kiss anymore.
"I know Britain has spent a huge amount of money on surveillance and I have been fascinated with it for some while, wondering who is behind the cameras, who is watching.
"They are amazing these cameras, they can zoom into your handbag."
Director of photography Robbie Ryan said he had been surprised by the quality of actual CCTV cameras, which could show action in high quality and were used in the film.
"They are very, very good cameras. We thought they would be black and white and fuzzy images.
"But they were high colour with good focus."
Mr Ryan admitted they had to make the CCTV footage in the film "look rough".
Red Road receives its gala premiere at Cannes on Saturday night.
Former US vice-president Al Gore is expected at the festival later to help promote environmental campaigning film An Inconvenient Truth.
The documentary is based on a series of lectures Mr Gore has given in the last few years.
The politician has accused the US of living in a "bubble of unreality" when it comes to global warming.