A bid to prevent child sex offenders from changing their name would have a "negligible" effect, Ministry of Justice officials say.
Parliament is considering National MP Jian Yang's private member's bill, which would prevent convicted paedophiles from registering a new name.
Legal advisers told a select committee today that it was unlikely to fulfil its intended purpose.
Ministry of Justice adviser Pasan Jayasinghe said there was no legal requirement to register a name to use it.
"A new identity is established simply when a person starts using a new name," he said.
Furthermore, a person was not legally obliged to provide their registered name or any other information unless it was specifically stated in law.
"This would mean that the bill's prohibition on child sex offenders changing their registered name will have a minimal impact practically on [their] ability to use other names," Mr Jayasinghe said.
It would not prevent paedophiles from committing identity fraud or from falsely using another person's name, officials said.
There were already more effective mechanisms for reducing the harm of child sex offenders, including intensive monitoring of high-risk offenders after release, vetting of all people working with children, and a proposed child sex offender register.
The bill has been found by Attorney-General Chris Finlayson to be inconsistent with the right to freedom of expression. Mr Finlayson found that there was no "rational connection" between the bill's objective and what it would achieve.
It was too wide in scope, capturing not only sex offenders but also some violent offenders -- the result of a drafting error which is expected to be amended.
Stopping offenders from changing their names was described as "disproportionate" by Ministry of Justice officials because it was permanent and non-discretionary. It could also hinder an offender's rehabilitation or reintegration into society, in particular offenders who were victims of child abuse themselves.
"In conclusion, the bill's limitation on the freedom of expression was found to be not justified," Mr Jayasinghe said.