A "strict liability" clause in the legislation means that it will not be a defence for a client to claim that he did not know of the woman's circumstances - effectively making it impossible for a man to know that he is not committing an offence when using a prostitute. The crackdown, which is modelled on similar policy in Sweden, was announced today by Home Secretary Jacqui Smith, who hopes that it will act as a severe deterrent to men who are considering paying for sex.