From the BBC:
Paying for sex with prostitutes who are controlled by pimps is set to become a criminal offence, [UK] 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.
This change is needed since it requires those who pay for sex to be responsible for the harm their actions do to victims of sex traffickers if they contribute to the harm done to those victims. A fine and a conviction won't stop all those who currently fund and motivate sex traffickers criminal actions, but it will cause some people to stop hiding behind deliberate ignorance.
The current system seems to be don't ask, can't tell. And it's not working.