THE Immigration Department has referred allegations of drug use at Villawood detention centre to NSW Police.

The referral follows the Opposition's attack on Immigration Minister Chris Evans for not seeking immediate police involvement.

Initially, Mr Evans said his department would investigate the allegations raised by former pastoral worker Pauline Lovitt and detainee Wilton Briggs.

The Age reported last week that Ms Lovitt saw detainees on "ice" and marijuana while working at Villawood from March to last month, and believed staff were involved in selling them.

"It is a very good move," said Ms Lovitt of the Government's response. "I do think it's in the best interests of the clients and the staff."

Mr Briggs, a New Zealander, has been under 24-hour surveillance since raising the allegations last week. He said he was threatened by a woman drug addict on Wednesday, because she was angry the drug supply inside Villawood could be affected.

The private company that runs Villawood, GSL, has denied drug problems at the centre, despite putting Mr Briggs under surveillance.

Mr Briggs, 29, said the drug addict threatened him and his partner and baby in Villawood's visitors' centre, but GSL officers did not restrain her.

Ms Lovitt said rehabilitation programs to help people in withdrawal must be introduced if there were a clampdown.

She urged the Federal Government to overhaul Villawood's management.

Detainees turned to drugs because they were given no help with their detention cases. Employees were under instruction not to help detainees — to the point where church workers must sign documents not to proselytise in case a detainee converted and it helped their case.

Ms Lovitt said resolving detainees' cases more quickly by offering them lawyers, translators and information would save money.

Labor's platform is to move Villawood, Australia's biggest mainland detention centre, into public management. It is yet to announce its plans for it.