Men who buy sex from women who have been coerced into prostitution or trafficked for sexual exploitation would be prosecuted under proposals to be announced by the Home Secretary tomorrow.

It would be an offence in England and Wales to pay for sex if the woman was being controlled by a pimp, had been coerced into the sex trade or was trafficked into Britain for sexual exploitation. Last year Jacqui Smith said: “We recognise that there is considerable support for us to do more to tackle the demand for prostitution and to prevent the trafficking of people for sexual exploitation.”

Gordon Brown recently indicated his determination to legislate in this area, when his spokesman said that he believed it was wrong for men to pay for sex.

The Home Secretary will make clear that the measure will not affect sole traders or women selling sex of their own free will. The move represents a compromise solution to demands from some senior members of the Government to criminalise the purchase of all sex. Police were concerned about the practicalities of a law banning any payment for sex.

Exact details of the new offence and the penalties to be imposed are yet to be worked out. Ministers believe that the measure will act as a deterrent to international human trafficking.

During a visit to Amsterdam as part of a government review of prostitution laws, Vernon Coaker, a Home Office minister, was told that the city was being used as a transit post for girls waiting to come to Britain to work as prostitutes.

The Government has toughened its stance on prostitution in recent years, after initially considering “tolerance zones”. Plans to permit small brothels, with two prostitutes and a maid, to operate legally remain under review.

Several years ago, Sweden criminalised buying sex but decriminalised selling it. Supporters of the scheme say it has sharply reduced the number of brothels and clients and the level of sex trafficking. Men who flout the law face a fine of 40 days’ salary, or a six-month jail term. Street prostitution has greatly fallen, officials say. But some critics have suggested that women who remain in the sex industry have become more vulnerable.

In Britain, Harriet Harman, the Minister for Women and Equality, was among those in the Government pressing for tough measures to tackle the demand for paid sex and to give greater protection for women. She wanted to make it illegal to pay for all sex. Under existing laws in Britain, prostitution is not illegal but keeping a brothel is a criminal offence. Kerb crawling and soliciting for sex are also illegal.

The Sexual Offences Act 2003 introduced penalties against those who sexually exploit children, and trafficking adults or children for the purposes of committing sexual offences was also outlawed. Latest police estimates suggest that as many as 18,000 trafficked victims are forced to work as prostitutes. Police projections vary from between 6,000 and 18,000.

Operation Pentameter 2, a six-month police campaign, has shown the extent of the sex trade industry. Figures released in July showed that 167 victims were rescued across Britain and Ireland and 528 suspected traffickers were arrested. The victims included 13 children aged between 14 and 17 who were rescued from sexual exploitation and two children who were under forced labour.

Paedophiles and other sex offenders will be compelled to take lie-detector tests under plans announced by the Government to bolster monitoring of their behaviour by the Probation Service. A total of 450 sex offenders who have been released from prison on licence will be tested over a three-year pilot scheme to begin in the Midlands next year. They will be asked a series of questions while their heart rate, perspiration, brain activity and blood pressure are monitored.

The questions are intended to discover if they have broken the terms of the licence under which they have been released from prison.

Ministers have legislated to allow polygraph testing to be included in a sex offender’s release licence and for such tests to be compulsory. Parliament could be asked for the scheme to be applied across England and Wales.

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