LONDON, Nov 19, 2008 (AFP) - Britain announced plans Wednesday to outlaw prostitution involving women forced into the sex trade through illegal trafficking -- but the move was sharply criticised by experts.

Home Secretary Jacqui Smith wants to criminalise paying for sex "controlled for another person's gain" in England and Wales after rejecting a total ban on prostitution because of insufficient public support.

Under current laws, buying or selling sex is not illegal but other activities related to prostitution, such as soliciting, kerb-crawling and pimping are.

"Trafficked women don't have a choice, men do... If there was not a demand for sex with trafficked women, there would be less trafficking."

Under the proposed changes, a man who pays for sex with a prostitute who has been trafficked will get a criminal record and could be liable for a fine of up to 1,000 pounds (1,190 euros, 1,500 dollars).

Not knowing that the prostitute had been trafficked or was being pimped will not be a defence in court.

Britain's laws on paying for sex have been in the spotlight since the murder of five prostitutes by a serial killer in Ipswich, eastern England, in 2006.

In recent years, the government has proposed a series of measures including relaxing the law by allowing groups of women to work together in brothels and introducing prostitution tolerance zones, later ditched.

Research from Exeter University in southwest England says there are around 80,000 prostitutes in Britain, of whom 20,000 have come from abroad.

Smith's plan is strongly opposed by the English Collective of Prostitutes (ECP), which represents sex workers and wants laws surrounding the trade to be loosened.

"Workers don't benefit from criminalisation -- the ECP has been inundated by women who have been raided, arrested and charged and face imprisonment for running safe, discrete premises where no coercion is taking place.

"Anti-trafficking legislation is being used to justify these raids... how can women who want to get out of prostitution find another job if they have a criminal record?" it said in a statement on its website.

A leading academic in the field has also spoken out against the proposal, accusing the government of "posture politics".

Belinda Brooks-Gordon, a reader in psychology and social policy at Birkbeck College, University of London, told AFP that a "tiny, tiny proportion" of people working in the British sex industry were trafficked.

"Nobody doubts that they are very vulnerable people in need of great help but this kind of sexual McCarthyism doesn't help those people," she said. "This will in effect be an all-out ban but it's a dishonest all-out ban."

The government is likely to include legislation which, if passed, would put the prostitution proposals into effect in the Queen's Speech -- the legislative programme for the next session of parliament -- on December 3.