Asian women are being snared in a student visa scam that funnels them into Sydney brothels where they are forced to sell sex and drugs for up to 20 hours a day.

A Sun-Herald investigation has found that after arriving in Australia on travel visas, dozens of women from Hong Kong and Thailand are being met by brothel managers who lodge study visa applications on their behalf. While most submissions fail, appeals are routinely lodged in the knowledge the process takes up to two years.

During that time, the women are at the mercy of traffickers who restrict their freedom and force them to work around the clock as prostitutes. While some are aware they are arriving to work in the sex industry, many are oblivious to the fact. Sources on the periphery of the sex ring have testified that within months, an increasing number of workers are finding themselves broken, battered and hooked on crystal meth (ice), which, in some parlours, they are obliged to offer to clients.

Despite detailed evidence having been lodged with the Department of Immigration more than a year ago, nothing has been done to close the visa loophole on which the scam thrives. While Blacktown police received a detailed tip-off about the drug epidemic inside two local brothels The Sun-Herald has recent audio recordings in which clients are still able to book girls who smoke ice as part of the service.

Commander of the NSW Police Sex Crimes squad, Detective Superintendent John Kerlatec, said: ''These are serious crimes and we work closely with our federal counterparts to ensure we tackle them not only in Australia, but offshore. The difficulty is in trying to get victimised witnesses to come forward.''

In February last year, consultancy firm Brothel Busters contacted two senior officials within Immigration's national investigation unit, identifying four Hong Kong women who were delivered to Australia to work in the sex industry. The girls were dispersed between two brothels in Blacktown and an associated parlour in Sydney's south. Brothel Busters head Chris Seage also provided a paper trail that demonstrated exactly how sex traffickers were utilising the student visa system. Three months later, a regular client of the Blacktown parlours became irate about prolific drug use on premises and turned whistleblower. In a letter, dated May 19, 2013, to Blacktown Council mayor Len Robinson, he stated: ''These working girls hardly speak a word of English … are here on a student visa and are permitted limited hours per week to work (20 hours) but are forced to work up to 18 hours a day.

''The brothel supplies, and the girls offer ice and ecstasy to their clients to make them stay longer.''

The customer even went as far as identifying three sex workers from whom ice and other drugs could be freely obtained, adding: ''These are not allegations but facts.''

Five days later, Mr Robinson wrote back stating ''regular inspections'' were ''routinely conducted'' by council inspectors. He added that because drug supply was a criminal matter ''beyond council's legislative authority to enforce'', the complaint had been sent to the ''superintendent'' of Blacktown police local area command.

Police responded with visits and referrals to federal authorities. However, two of the three women identified by the whistleblower are still rostered on.

In 2012-13, 3446 appeals against refusals were lodged from 290,761 student visa applications submitted over the same period. A spokesman for Immigration Minister Scott Morrison said the ''vast majority'' of student visa applications were approved. ''Overhauling the student visa system would not prevent unscrupulous individuals from seeking to use this or other visa programs to profit from trafficking or trafficking-like activities,'' he said.

Allegations of sexual exploitation through student visas stretch back to at least February 2012, when the Australian Federal Police arrested the Chinese-Cambodian owner of the Diamonds 4 Ever brothel in Guildford.

Song Ea, 42, faces two charges of organising entry reckless as to exploitation, two counts of employing a non-citizen to work in breach of visa condition and conducting business involving sexual servitude. He is due to appear before Sydney District Court on Friday.

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