The government's new prostitution proposals have been criticised as unenforceable, by the UK's head of anti-trafficking.
The new measures, announced last month by home secretary Jacqui Smith, would mean that men would be breaking the law if they paid for sex with a woman trafficked into the UK or is working for a pimp, regardless of whether the man was aware the woman was forced into prostitution.
Commander Allan Gibson, head of the Met's anti-trafficking unit, said to the Commons home affairs committee: "Speaking personally, I think that is going to be very difficult to enforce."
Committee chairman Keith Vaz told minister for women Harriet Harman: "[Commander Gibson] says it is very difficult to enforce a situation where a man is expected to ask a prostitute whether or not she has been trafficked and even if he gets a negative answer he is still to be prosecuted.
"The police themselves... feel that the new proposals are unenforceable."
That sentiment has been echoed by Chris Huhne, Liberal Democrat home affairs spokesman, who said the new measures will force these vulnerable women further underground.
Mr Huhne said: "The Finnish system of criminalising the clients of exploited and trafficked women is a bad model. It has had a poor record of successful prosecutions, precisely because the women deny a problem and juries are reluctant to convict when the client says they were misled.
"The government's other proposals run the risk of driving already vulnerable women underground and into the hands of pimps and pushers."
The new measures are based on the laws currently operating in Finland which have been in place since 2006.