TV watchdog Ofcom has warned broadcasters about airing violence before the watershed and announced that it will commission research into the issue, as Channel 4 soap Hollyoaks was found to have breached programme rules.

The regulator will look at viewers' attitudes towards on-screen violence, assessing whether the amount of violence on British TV has increased.

It 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".

Hollyoaks breached broadcasting rules in an episode, screened at 6.30pm in March, in which a main character was killed by a speeding train.

Channel 4 said viewers were notified that a dramatic episode would be broadcast but Ofcom 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 scenes which followed."