British Prime Minister David Cameron has warned that easy access to web porn is "corroding childhood".
And with children as young as five being reported to the police for sex offences, the National Society for the Prevention of Cruelty to Children has said online pornography is warping youngsters' ideas about sex and relationships.
The latest survey also found that 90 per cent of young women who view porn do so over the web, with free sites the most popular. Many access it in more than one way, with some 40 per cent said they read erotic stories, a figure likely to have been boosted by the popularity of the Fifty Shades of Grey series.
Just three per cent said they view adult material in magazines. When asked which devices they use to view pornography, 62 per cent said their smartphone.
Laptops were the next most popular, followed by iPads and desktop computers.
The survey reflects how technology has changed how people access X-rated material.
According to firm Covenant Eyes, which provides internet filtering, as many as one in five mobile searches are for porn - and 24 per cent of smartphone owners admit to having pornographic material on their mobile handset.
Many of the women who responded to the Marie Claire survey said viewing pornography enhanced their sex life.
Writing in the magazine, Miss de Cadenet, 43, said: "Porn is here to stay and we have to learn to negotiate it."
Some 20 per cent of those surveyed said they felt embarrassed and ashamed and 41 per cent said that didn't want anyone to know about their habit, while two-thirds said they only ever watched porn alone.
- Daily Mail