London - Ellie Chapman was using her laptop to update her CV in the local library when her attention was first drawn to a man using a public computer a few feet away.
In his early 60s, he had his back to her but his screen was very much in 23-year-old Ellie’s line of sight. And on it was content no one should expect to see in a public library.
Glancing up from her work, Ellie was stunned to realise the man was watching images that could only be described as pornographic.
"I couldn’t believe it - it was absolutely awful," says Ellie, who’d only just moved to her new place and was using the library because she’d not yet got broadband at home.
"And to make it worse, he kept adjusting his crotch area. I don’t think he realised I was sitting behind him, because when anyone else walked past he would quickly switch screens to look at his email."
That anyone would consider it appropriate to view pornographic content in a public library demonstrates a flagrant disregard for the sensibilities of others, yet such behaviour is becoming increasingly prevalent.
Ellie later learned the man was a library "regular".
On public transport, where it is not uncommon for women to find themselves travelling alone at night, the experience can be chilling.
Natalia Grigoriou, 25, a teacher who lives in North London, was at a bus stop at 8.30pm one evening in January this year when she realised the man next to her was watching porn on his phone.
"We were probably waiting for the same bus," she says, "and at first I thought he was slightly tipsy. But then he answered his phone and seemed to be able to talk normally, which reassured me.
"When he ended the call, he sat down again and all of a sudden I heard women moaning and groaning. Instinctively, I turned my head and saw what he was watching - I just couldn’t believe it.
"He realised then I could see and hear what he was watching, but rather than switch it off, he put in some headphones and carried on."
Matters escalated when the bus arrived and the man sat opposite Natalia. He continued to watch and began to touch himself intimately.
The pace of technological advance has made access to pornography frighteningly easy - as simple as a tap on a smartphone screen. It’s been estimated that as many as one in four clicks are porn-related.
But what makes anyone think that it is acceptable to inflict their viewing on those around them?
Suzie Hayman, a counsellor, agony aunt and trustee of the charity Family Lives, says: "If we go back even just 15 years, porn was something you had to put quite an effort into obtaining: it was a brown paper package, the top shelf, it wasn’t easy. There was a certain amount of shame attached because of the effort you had to put in.
"Fast forward to now and it is the ease of delivery that I think has made it all so mainstream."
She maintains the crossover of fashion choices and dance moves once associated with the sex industry into the mainstream as another factor in normalising the viewing of pornography.
And, of course, the more an action is repeated by other members of a group, the more normal and acceptable that action becomes.
Last year, security experts Norton by Symantec reported that a survey indicated as many as one in six people had used public Wi-Fi to view adult content.
The damaging effects of the proliferation of pornography have been well documented, with children being particularly vulnerable to its effects.
Hayman says this in itself is dangerous. "A lot of pornography is violent, abusive and transgressive, and it objectifies women.
"Young men are picking up the message that your own satisfaction is what’s important, that the woman will give in; that it’s okay, everyone else is doing it. And that’s the message girls are getting, too."
Adults, too, are damaged by the spread of porn, with couples reporting sexual problems and increased isolation. But are the men who choose to watch porn in public doing so for some kind of twisted sexual gratification?
Dr Thaddeus Birchard, clinical director of the Marylebone Centre for Psychological Therapies, says some men may be doing so as a way of shocking or attracting women. In other cases, he adds, it may be as simple as male brain chemistry at play.
"The brain chemistry of arousal, particularly in men, shuts down the capacity to consider consequences. Just think of Bill Clinton."