The deals, which are legal, are on classified ad sites such as craigslist.
Charities have described the adverts as exploitative and Hove MP Peter Kyle wants them made illegal. Craigslist, which on one day carried more than 100 such adverts, has not commented.
One student described how she felt her only option was a “sex-for-rent” deal.
The woman said: “He took me into his living room, got me drinks, and then after that it was just straight upstairs and go for it.”
And she continued: “He would do what he wanted to do, forcefully, and I just sort of went along with it – after the third time, I started feeling physic
Adverts seen by BBC South East included one posted by a Maidstone man asking for a woman to move in and pretend to be his girlfriend, another publicising a double room available in Rochester in exchange for “services” and one in Brighton targeting younger men.
One advert posted by a London landlord asked for a “naughty girl” to move in.
Landlords who posted the adverts were clear how the arrangement would work.
One said: “I was thinking once a week, something like that, I’m happy as long as there’s sex involved.”
Another said: “You agree sort of like a couple of times a week, pop into my room sort of thing, but as far as the apartment’s concerned, it’s like completely as if we’re flatmates. It’s all the bills, the rent, free.”
Mel Potter, from woman Brighton Oasis Project, a women’s charity, warned of the dangers. She said: “It’s something that potentially can trap someone and put them at risk of violence and abuse.”
Andrew Wallis, of anti-slavery charity Unseen, said: “I think these adverts go as close to the edge of the law that they possibly can without breaking the law.
“They would argue that they have chosen voluntarily to enter that situation.
“The trouble is when you have a vulnerable person who then becomes exploited, the concept of choice soon disappears.”
One landlord defended the deals as a “friend with benefits” arrangement.
He said: “You can argue that high rent charged by landlords is taking advantage too. There’s no compulsion for them to do this. Everyone goes into it with their eyes wide open.
“I am the last type of person who’d like to take advantage. Both sides have something the other person wants. I see it as a win-win situation.”
Paul Noblet, from homeless charity Centrepoint, suggested website owners could consider a voluntary code under which they could monitor and remove such adverts.
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