Channel 4 soap Hollyoaks broke the rules when it broadcast a “violent and shocking” scene where a main character was killed by a speeding train, the media watchdog has found.
Ofcom issued a stern warning to broadcasters about airing violence before the watershed and announced that it will commission research into viewers' attitudes towards on-screen violence.
Hollyoaks was found to have breached programme rules in an episode broadcast at 6.30pm on 19 March 2013.
The episode showed former drug dealer Brendan Brady (played by Emmett J Scanlan) pushing arch nemesis undercover policeman Simon Walker (Neil Newbon) into the path of a train, resulting in his death.
Walker was shown screaming as he fell backwards on to the railway track before the camera cut away to show the train passing at high speed.
Channel 4 said in its defence that it had taken a number of measure to ensure the scene complied with Ofcom’s rules.
The scene marked the culmination of a long-running revenge storyline and Channel 4 said "there was an expectation from viewers that there would be a dramatic end to such a complex tense relationship".
But Ofcom today issued a statement to "remind television broadcasters of the need to ensure that all material broadcast pre-watershed which features violent scenes is appropriately limited".
The TV watchdog plans to assess whether the amount of violence on British TV in everything from documentaries to dramas has increased over the decades, looking specifically at shows scheduled before and immediately after the 9pm watershed.
"Broadcasters should consider whether individual acts of violence within a programme are suitable, as well as where the overall tone is malevolent, menacing and threatening, that this also remains suitably limited," it said.
Channel 4 showed no images of Walker being hit by the train during the minute-and-a-half-long sequence. But build-up included a fight showing several blows to the face and stomach, Brendan's head being pushed through railings and Walker with bloody lips and blood running from his nose.
Channel 4 said that the storyline had run for around a year and that viewers were notified that a dramatic episode would be broadcast. It said that the fight scene only lasted around a minute, was at the end of the episode and carefully edited.
Ofcom said that it accepted that violence was "a part of life and integral to many dramas, including those broadcast pre-watershed."
But it said that the pre-programme information was too vague and would "not have prepared the significant number of younger viewers in the audience, or their parents, adequately for the violent, intense and shocking scenes which followed."
It said: "This scene was both violent and shocking and had the potential to distress younger viewers as well as raise concerns about the level of violence amongst parents watching with their children regardless of the editorial context presented or the signposting provided. For all these reasons Ofcom considered that it was unsuitable for children."
It said that research, carried out in 2010, showed that parents' biggest concerns about pre-watershed content was violence, sexually explicit content and offensive language. Soaps were the programmes which caused most concern.
Channel 4 argued that Hollyoaks, which regularly deals with storylines about sexual abuse, domestic violence and drugs, was aimed at a teenage audience.
But Ofcom said figures showed that 15 per cent of the audience of the train death episode were children aged four to 15 and 10 per cent were aged four to nine.
The watchdog "concluded that cumulatively the violent content in this sequence exceeded viewers' expectations for a drama transmitted long before the watershed when young children were available to view and in this case were watching in large numbers".
Tony Close, Ofcom’s director of content standards, said: "Broadcasters have a duty to protect children from violent material. The rules in this area are very clear, making it unacceptable for any broadcaster to include scenes of violence that are unsuitable for children before the watershed.
"The protection of under-18s from potentially harmful content is a key area of concern for Ofcom. As such we have commissioned new research into viewers' attitudes to violence on television.
"This will further inform us about the level of concern about violence on television - and will contribute to our ongoing work on the enforcement of the 9pm watershed."
Additional reporting from PA