Jacqui Smith says she is concerned about vulnerable women
Paying for sex with prostitutes who are controlled by pimps is set to become a criminal offence in England and Wales, Home Secretary Jacqui Smith said.
Anyone who knowingly pays illegally trafficked women for sex could face rape charges, while kerb crawlers could face prosecution for a first offence.
There will also be more "naming and shaming" of kerb crawlers and new police powers to close brothels.
Buying or selling sex is legal but soliciting and pimping are not.
The changes bring the law in England and Wales more into line with Scotland, where anyone looking to pick up a prostitute faces a fine of up to £1,000.
Ms Smith said the government had considered banning paying for sex altogether but had ruled this out as there was no public support for such a move.
Instead, she said the government's efforts would be focused on reducing demand for trafficked women, who were "effectively held as slaves", and there would be a marketing campaign aimed at men who used prostitutes.
We want to send a clear message to force men to think twice before sex
She told BBC Radio 4's Today programme: "My proposal is that men should think twice about paying for sex. The reason they should do that is actually the majority of women don't want to be involved in prostitution."
She added: "Trafficked women don't have a choice, men do."
Ms Smith said up to 70% of prostitutes were controlled by pimps or had been trafficked into the country and the government was working closely with the police on plans to enforce the new laws.
But Nikki Adams, of the English Collective of Prostitutes, said the government had "made up" the number of women being trafficked into the UK and most prostitution was "consenting sex".
Under the plan, 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.
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.
Separate proposals will soon be published to place lapdancing clubs under the same licensing arrangements as sex shops, rather than as pubs and bars as at present.
This would allow people living nearby more chance to raise objections.
For the Conservatives, shadow home secretary Dominic Grieve said: "The government's proposals will not protect the most vulnerable victims.
"Rather than creating new laws, the home secretary should focus on enforcing existing laws."
Liberal Democrat home affairs spokesman Chris Huhne said: "Help for the victims would be more convincing if the government hadn't slashed the budget for human trafficking investigations last week and shut down the leading unit.
"The proposal to close brothels runs the risk of driving already vulnerable women underground and into the hands of pimps and pushers."
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.
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