The watershed, which continues to be a vital tool in protecting young TV viewers, is 50 years old this month.
In July 1964, Parliament passed the law that led to measures to protect children from seeing harmful or offensive material on TV in the evenings.
Fifty years on, new Ofcom research shows that most adult TV viewers are aware of the 9pm watershed as a valued way of indicating what is suitable for young viewers.
When the watershed was introduced, broadcasters were scheduling programmes such as Z Cars and Dixon of Dock Green. While many of these TV programmes have long since disappeared, the watershed - now enforced by Ofcom - remains a widely understood means of protecting children.
Ofcom's research shows that 98% of adults in the UK watch TV. Among TV viewers, 94% are aware that the watershed requires broadcasters only to show programmes unsuitable for children after a certain time (compared to 91% in 2008).
Today, more TV viewers believe the watershed is at about the right time (78% in 2013 compared to 70% in 2008), Ofcom's report on UK audience attitudes to broadcast media shows. When asking parents who watch TV whether the watershed is at about the right time, this increases to 80%, compared to 72% in 2008.
Similar proportions of adults who watch TV believe that it should be the responsibility of 'both broadcasters and parents equally' (49%) and 'mainly parents' (46%) to ensure children do not see unsuitable programming.
With over a third (37%) of children aged 5-15 with internet at home now watching �'on-demand' content, Ofcom is working with Government and industry to examine how TV protections will continue to apply in a digital world.
Ofcom has a duty to protect viewers, especially children, from harmful and offensive content on TV. If broadcasters show programmes that break the rules, Ofcom imposes sanctions, including fines.
Watershed rules state that the transition to more adult material after 9pm must not be unduly abrupt, and the strongest material should appear later in the evening. But even then, Ofcom's rules protect viewers from harmful and offensive content.
Understanding audience attitudes and expectations supports Ofcom in its role in protecting all viewers.
In the past five years, there have been falls in the number of viewers saying there is 'too much' violence (35% of adult viewers in 2013, down from 55% in 2008), sex (26% in 2013 versus 35% in 2008) and swearing (35% in 2013 versus 53% in 2008) on TV.
One reason for this is a change in attitude among older viewers. The number of viewers over 65 who believe there is too much swearing (78% in 2008 compared to 55% in 2013) and violence (75% in 2008 compared to 52% in 2013) has fallen over the past five years.
Among those adults who had been offended by something on TV in the last 12 months (18% of adult viewers), nearly four times more people are likely to continue watching the programme than in 2008 (5% in 2008 versus 19% in 2013) and less likely to turn off the TV altogether (32% in 2008 compared to 19% in 2013).
While on-demand TV is estimated to account for only 2.5% of TV viewing, Ofcom recognises this poses new challenges.
Ofcom is working with Government, other regulators and industry to ensure that children remain protected if they choose on-demand TV over traditional broadcast TV, where Ofcom's strict watershed rules apply.
This would mean that consumers have a clear understanding of the protections that apply on different platforms and devices, and know which regulatory body to turn to if they have any concerns.
Tony Close, Director of Standards at Ofcom, said: "Fifty years on, the TV watershed remains a vital means of protecting viewers.
"While attitudes have changed over the decades, Ofcom ensures that TV standards meet the expectations of viewers. We take robust enforcement action when the rules are broken, which reflects the importance we place on protecting children."
Claudio Pollack, Director of Ofcom's Consumer and Content Group, said: "Ofcom recognises that the growth of on-demand TV is posing new challenges for parents and regulators.
"We're working on ways to help ensure that the protections viewers expect from the watershed apply beyond broadcast TV."