At 11pm on 3 November 2009 in the House of Lords parliament took a significant step to protect women exploited in prostitution. It is going to be a crime to pay for sex with a woman or man who is subject to force, coercion or exploitation.

The implications of this legal change are enormous. It puts the responsibility for prostitution on to the purchaser, who has a choice, instead of a seller who does not. I believe it will also protect communities where prostitutes work who have little choice about what is occurring on their doorstep.

The campaign for this change has dominated two years of my life. When I was a Home Office minister with responsibility for prostitution policy, I recognised that policy changes should protect women. Prostitutes face daily danger: study after study shows most have been physically assaulted, or raped, and show symptoms of PTSD.

So I proposed that when two women work together as prostitutes they should not be prosecuted for brothel keeping, which is an offence of exploitation. That got me dubbed ‘Madame Minister.’ 

But because prostitution is so dangerous and exploitative we need to reduce it. The average age of entry to prostitution in Britain is 15 and vulnerable children need help to avoid being prostituted. Women also need help to exit into alternative employment.

Tackling supply is not enough; we need to do more to deal with demand. When I left the Home Office I tried to find what country had made a better job of dealing with the issue of demand.

Examples of decriminalisation were depressing; in places like Amsterdam tolerance zones had merely increased the market for prostitution and created sex tourism without reducing exploitation and criminality.

Sweden was the place which had made the most difference. In 1999 they passed a law which decriminalised the prostitute women and which made the would-be purchasers of sexual services into criminals.

I started campaigning for a similar approach in Britain. Research demonstrated that such a radical change would win support if it could be shown to reduce trafficking as it had in Sweden. The appointment of a woman home secretary made change more possible.

The approach she adopted did not go as far as Sweden, but made it a strict liability offence (ie ignorance is not a defence) for a man to pay for the sexual services of a woman who has been exploited or forced.

A strong group of voluntary organisations got behind the campaign, at the start the Lords showed more sympathy for clients than women who had been bullied into prostitution and it was only at the last minute they backed the change.

Passing the law is not the same as implementing it and it will be up to police and magistrates to make it work.  Publicity is also key, so people can change their behaviour. Trafficking of human beings is vilely exploitative, when this law is in force British men must no longer escape responsibility when they pay for sex with trafficked or coerced women.