Calls by police to criminalise off-street prostitution have been criticised as appalling and dangerous.
Street prostitution in Nottingham has decreased by 80% over the past decade, police say, but they believe there has been an increase in off-street work.
Nottinghamshire Police has said a law change would allow officers to arrest clients approaching sex workers in private premises.
But a group representing sex workers said it would make work more dangerous.
Current legislation makes it an offence to solicit a person for obtaining sexual services in a public street.
However, Sgt Neil Radford, the head of Nottingham's prostitution task force, said: "On the street, the law allows you to deal with people who are purchasing sex.
"But there is no equivalent legislation for off-street work. If somebody goes into a brothel to purchase sex, it is possible he isn't committing any offence at all.
"That's wrong and we have to be able to do something about it."
Sgt Radford also claimed such a law change would help reduce the demand for trafficked women and children.
However, the English Prostitution Collective, an organisation of sex workers, said: "We are appalled that the best the police can come up with is a proposal to increase criminalisation.
"These proposals will further divert police time and resources from investigating rape, trafficking and other violent crimes to policing consenting sex.
"Criminalising clients will not stop prostitution, nor will it stop the criminalisation of women. But it will make it more dangerous and stigmatising for sex workers.
"Sex workers on the street and in premises will find it harder to screen clients who will want to remain anonymous because of fear of arrest."
She added the group was campaigning for decriminalisation so sex workers could report violence without fear of being arrested.
Nottingham's sex trade
women in the city sell sex online
4 successful convictions for rape on street sex workers
0 convictions for attacks on prostitutes working off street
Nottingham charity POW, which supports sex workers, said there are more than 400 adverts online offering off-street sex in the city.
Daniela Scotece, the charity's chief executive, said: "The internet is the fastest-growing outlet offering sex for sale.
"There are concerns there are safety implications with this. If somebody is working from the street and they see somebody they don't like the look of, they get the chance to walk away.
"But if they are just opening the door to somebody, that risk assessment procedure is gone."
For more on this subject, watch Inside Out on BBC One East Midlands at 19:30 on Monday 26 October and nationwide for 30 days thereafter on the iPlayer.