Detention centre operators, an international training company, a NSW Government department and a multinational IT firm are the big winners from the Federal Government's immigration policies.

An analysis of tender data by The Canberra Times has identified, for the first time, the companies that have won the most lucrative contracts from the Department of Immigration and Citizenship since 2008.

Combined with information from DIAC, a fuller picture has emerged of the true cost of the Federal Government's asylum-seeker policy, with a refugee advocate saying the money could be better deployed in cheaper community-based alternatives.

The tenders data shows that multinational detention centre operators G4S and Serco have been the biggest financial beneficiaries of the Federal Government's mandatory detention policies.

Detention centre operator Serco tops the list, thanks to its five-year contract to run Australia's immigration detention network. The contract, worth $279million in 2009, was quietly revised upwards to $712million in July.

Serco also has another contract worth $44million to provide ''Immigration Residential Housing and Immigration Transit'' to DIAC.

Serco won the tender from rival G4S, which had been running the detention centres since 2003 under a $580million contract.

The next big winners were global education provider Navitas English, which has signed $460million in contracts with DIAC, and the NSW Adult Migrant English Service, part of the NSW Department of Education and Training, which has signed $347million in contracts since 2008.

Information technology services provider IBM has entered into or varied hundreds of contracts worth a combined $312million.

Another big winner is International Health and Medical Services, which has contracts worth $293million to provide services for Christmas Island and mainland detention centres.

The scale of the cost of Australia's asylum-seeker policies was further highlighted last month when DIAC told a parliamentary committee that it cost $772million in 2010-11 to run Australia's main detention centres.

A department spokeswoman said the Government ''has always acknowledged that immigration detention is expensive''.

''We take our duty of care to provide appropriate accommodation and conditions for people in immigration detention seriously,'' the spokeswoman said. ''Higher numbers of people in immigration detention have an impact.''

DIAC said yesterday that as of September 8, 4873 boat people and crew members were being held in Christmas Island and mainland detention facilities. This did not include the boat, carrying 72 people, which landed on Friday.

In June, 6403 people were being held in immigration detention.

The department expects the cost of detaining asylum-seekers to fall in the current financial year to $628.7million. It says the cost of running the Curtin detention centre - this year $108million - will fall $20million next year.

Asylum Seeker Resource Centre chief executive Kon Karapanagiotidis said his non-profit organisation cared for asylum-seekers in the community for just $4.80 per person per day, providing food, public transport, legal services, a GP, and other services.

He called for the current debate about onshore and offshore processing of asylum claims to be re-cast. ''Both are unviable options,'' he said. ''We think the alternative is community-based alternatives. We're wasting billions.''

In 2010-11 community detention cost the Government $15.7million.

The DIAC spokeswoman said it was meaningless to compare the the two models, but she acknowledged that community-based options were reducing cost pressures on the detention network.

By Friday, Mr Bowen had approved 1882 people to be transferred into community-based detention.