Paying for sex with prostitutes who are controlled by pimps is set to become a criminal offence, Home Secretary Jacqui Smith is expected to announce.
She will also say that people who knowingly pay illegally trafficked women for sex could face rape charges.
Ms Smith is to promise that more kerb-crawlers will be prosecuted and police will get powers to close brothels.
Buying or selling sex is legal but many prostitution-related activities, such as soliciting and pimping, are not.
The Home Office is planning to criminalise paying for sex with a woman "controlled for another person's gain".
Those convicted would get a fine and a criminal record
Pleading ignorance of the circumstances under which a prostitute is working will not count as a defence.
A Home Office spokeswoman said: "We want to do everything we can to protect vulnerable women.
"That is why we are determined to shift the focus onto the sex buyer, the person responsible for creating the demand for prostitution markets which in turn creates demand for the vile trade of women to be trafficked for sexual exploitation."
She added: "We want to send a clear message to force men to think twice before sex and make it clear that if they pay for sex with someone who has been controlled or exploited, they will get a criminal record and a hefty fine."
Under the plans, people who pay a prostitute for sex knowing they have been trafficked against their will could be charged with rape.
Ms Smith will promise that kerb-crawling will be punishable the first time a person is caught doing it, rather than just persistent offenders.
The Home Office said police would get powers to close brothels.
Currently they can only shut premises associated with prostitution if anti-social behaviour or when Class A drugs are involved.
Critics of the government's proposals say they will simply drive customers elsewhere, rather than tackling the problem.
Under the Home Office plans, lapdancing clubs would be subjected to the same licensing laws as sex shops, rather than pubs and bars, as at present.
HAVE YOUR SAY The only way to help prostitutes is to legalise the trade and have proper red light districts Neil, Liverpool
This would allow people living nearby more chance to raise objections.
The Sexual Offences Act 2003 made it illegal to buy sex from anyone aged under 18 and introduced penalties for trafficking adults and children for the purposes of sexual exploitation.
It is not illegal for someone aged over 18 to work as a prostitute in off-street premises but where there is more than one prostitute, the owner of the premises can be prosecuted for keeping a brothel.
Many of the activities associated with street prostitution, such as soliciting and kerb-crawling, are also illegal and it is against the law to advertise sexual services on cards in telephone boxes.
In December last year, Women's Minister Harriet Harman said paying for sex should be outlawed.
6 months ago