They say the deals take advantage of those unable to afford spiralling rents and "go as close to the edge of the law…without breaking [it]".
Websites hosting adverts for such offers are being urged to tackle the problem.
As young people and the low-paid are priced out of accommodation, particularly in south-east England, "sex for rent" adverts have sprung up online.
One classified advertising site, Craigslist carried more than 100 such listings in a single day, a BBC investigation found.
A female student who answered one of them said she felt it was her only option.
She added: "He took me into his living room, got me drinks, and then after that it was just straight upstairs…He would do what he wanted, forcefully, and I just sort of went along with it."
Labour MP Peter Kyle said classified websites should stop allowing the adverts or Parliament should intervene.
"If [websites] don’t stand up to this and then accept their responsibility, I will be pushing for legislation to do it for them," he said.
A string of charities have backed his calls for a crackdown.
Mel Potter, of the Brighton Oasis Project for women, 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, added: "I think these adverts go as close to the edge of the law that they possibly can without breaking the law.
"The [landlords] would argue they [tenants] 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."
Paul Noblet, of homeless charity Centrepoint, called for advertising sites to consider a "voluntary code" under which the offending posts could be removed.
One of the adverts on Craigslist, from the owner of a "small two-bedroom house near Hull", says: "Money is not an issue, I would prefer some company.
"There are some stipulations to the living arrangements…This would be a mutual benefits arrangement. Free rent, paid in other methods."
Meanwhile, a "City worker" living in a ‘luxurious spacious apartment’ in central London was seeking ‘a dominant attractive woman who in return will place me beneath her beautiful feet and boss me around’.
The 35-year-old asked anyone interested to send photos of themselves and their "lovely feet".
Other adverts included a man in Maidstone, Kent, seeking a woman to move in and pretend to be his girlfriend.
A double room in Rochester, Kent, was said to be available in exchange for unspecified "services", while younger men were targeted by a post from a Brighton property owner. An "open-minded naughty sexy girl" was requested by a London landlord, who added: "Send your pictures, age, name, maybe nationality… Room can be used to work from like massage etc or just to live in."
One landlord told the BBC: "I was thinking once a week, something like that, I’m happy as long as there’s sex involved."
Another said: "As far as the apartment’s concerned, it’s as if we’re flatmates. It’s all the bills, the rent, free."
But he added: "You agree sort of like a couple of times a week, pop into my room sort of thing."
A landlord who defended the arrangement as a "friend with benefits" situation, added: "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."
He rejected claims it could be construed as sexual exploitation, saying that people working in jobs they did not enjoy was "like a form of prostitution".
Craigslist did not respond to requests for comment.