The number of viewers who believe there is too much sex, violence and swearing on TV has fallen sharply, according to new research by broadcasting regulator Ofcom.

More than half of viewers (55%) believed there was excessive violence five years ago, but that figure has now fallen to 35%.

The figure for those who think there is too much sex has fallen from 35% to 26% over the same period, while swearing is a concern for 35%, down from 53%.

The study also found awareness of the TV watershed, designed to protect children from unsuitable scenes before 9pm, continues to be high.

It found 94% of viewers knew of the watershed - established 50 years ago this month - which is up from 91% when comparable research was conducted five years earlier. The study also found 78% thought it was at about the right time, a rise from the previous 70%.

Ofcom said a change in attitudes among older viewers is one of the reasons for the figures for sex, violence and swearing dropping markedly.

The regulator acknowledged that on-demand and catch-up viewing will prove a "new challenge" in terms of protecting children using the watershed concept, although it pointed out that such services account for only 2.5% of viewing at present.

Tony Close, director of standards at Ofcom, said: "Fifty years on, the TV watershed remains a vital means of protecting 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."