The 480 residents with intellectual disabilities living at the prime site in Melbourne's inner-east would be rehoused in new accommodation; the government's joint venture partner would make a handy profit for his trouble; the state would cover the cost of relocating the former residents and share in the profit, yielding millions of extra dollars to pour back into wider disability services.

Ten years later, as the deal comes to an end, there appears to be one clear winner - Lang Walker, the multi-billionaire property developer from Sydney's North Shore.

Those with disabilities who lived on the site are understood to be happy enough with the outcome, though their former parkland home is now an enclave for the well-heeled.

But the mini bonanza for other disability services never eventuated.

For the state, revenue from the sale of houses with price tags up to $3.85 million has fallen well short of the more than $100 million public cost* of rehousing the former Kew residents. The "profit-share" deal with the developer was a fizzer.

Mr Walker has made profits but just how much is unclear. From the accounts they appear modest, but property experts say they may in reality be in the hundreds of millions of dollars. Neither Mr Walker nor the government will discuss costs or private profits.

The state's poor financial outcome from Kew raises questions about the contracting and management of public-private ventures - especially when big political donations are in play. And it begs the question: how could a government do so badly on its own premium real estate in a well-serviced location overlooking the Yarra River and central city amid tree-lined streets and private schools?

"The Kew project was supposed to be the revitalisation of disability services," said Max Jackson, a disability sector expert and former chief executive of the Kew Cottages complex.

"Standing on the periphery of the redevelopment it appears that transparency has been the loser, and Walker the big winner."

When former premier Steve Bracks first announced the redevelopment of the old Kew "asylum" in 2001, he envisaged an outright $100 million* land sale and a "flagship" housing project. It was to be a model of de-institutionalisation, with most of the former residents rehoused in the wider community but about 100 to remain on site in new group homes.

Soon the plan would change and, rather than a straight sale, a private partner would be sought for a development joint venture. Walker was chosen in mid-2005. Then community services minister Sherryl Garbutt painted a picture of returns enough for "high-quality housing and support services for [Kew] residents and other people with a disability in the community".

At the scheduled end of the Walker contract in late 2016, Mr Walker's development company had made total revenue from house sales of $520 million, but the state had received just $54 million, way short of what Steve Bracks and his ministers had imagined. This is a little more than the agreed base land price for the 27-hectare site in 2006, a surprisingly low amount ($30.9 million in 2006 dollars).

The government agreed to take less up front in return for a 50 per cent share in any profit made by Walker Corp after the company had taken out 18 per cent return on its costs.

To date, the profit share has delivered zero to the state. The Age has established that the government expects not a cent from it, even when the contract ends. (It has been extended to April 2018 at the request of the developer who is seeking new approvals for a small apartment complex.)

A leaked 2013 summary of the project based on Walker's financial models, may help explain the failure of the profit-share deal. It points to a big blow-out in the costs claimed by Walker.

The summary shows that, by 2013, the original estimated cost to develop each dwelling of $657,000 had doubled to almost $1.4 million. This allowed Mr Walker's Kew Development Corporation to report only small profits - not enough to reach the 18 per cent hurdle for the profit share.

Notably, the leaked assessment reveals that costs per dwelling claimed by Walker included an average of almost $600,000 per dwelling for "other" non-construction costs. That is, almost half the developer's costs appear to be for civil works, architects, heritage, consultants and other expenses not directly related to the building of homes.

Neither the government nor Mr Walker will explain the dramatic hike in costs and whether, for instance, they may include elaborate expenses, such as the cost of Lang Walker doing business via private jet.

The government's development agency, Major Projects Victoria, will only confirm that Walker's stated profits have been less than the government's $54 million return to date. Other than that, it says its partner's finances are confidential.

It is a curious response given that Walker Corp itself, through its special purpose Kew Development Corporation subsidiary, has reported Kew project costs and profits to the corporate regulator, ASIC, for the years 2012-2015.

The reports reveal sales revenue totalling almost $296.4 million but costs of $250.9 million, or 85 per cent over the four-year period.

Property experts and other sources familiar with the project query the costs claimed. They believe Mr Walker, renowned for his business savvy, his political clout, and Sunday morning coffees with former NSW MP Eddie Obeid, may in reality have made windfall profits from the scheme.

Peter Hay is a senior land valuer with 30 years' experience working in the property industry and for government. He knows the Kew development well and has done valuations for clients buying into the new neighbourhood.

On behalf of The Sunday Age he calculated the costs and potential profits based on his own research and publicly available information.

Hay estimates that the all-up cost of developing and building at Kew would be an absolute maximum of $260 to $300 million, a figure that includes a commercial land price and standard builder profits. His assessment leaves up to $260 million unaccounted for given the $520 million in total sales.

"This is not a good result for taxpayers," says Hay. "Where's all the money gone?"

Hay says the state should have got double the land value to begin with, and a substantial profit share. "It seems the developer got the land cheap and then inflated their costs."

Another expert, with intimate knowledge of the Kew project, insists the total project costs could be no more than $337 million, leaving the possibility of a windfall of $180 million.

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Lang Walker, 71

• Sydney North Shore-based developer prominent in the property industry for more than 50 years
• Number 17 on 2016 BRW rich list with personal wealth of $2.02 billion
• His Walker Group Holdings made $246 million profit (46% profit margin) in 2015-16
• Has delivered more than 1000 projects including the $2.5 billion Collins Square complex in Melbourne's Docklands and the Kew Cottages redevelopment
• Awarded an Order of Australia Officer (AO) in 2015 for his philanthropic work including in social welfare, health and heritage
• Known for his use of a private jet for business
• Owns a fleet of yachts
• A one-time regular Sunday morning coffee companion of ex-NSW Labor MP, Eddie Obeid
• A major political donor, tipping more than $2 million into Liberal and Labor parties nationwide since 1999 including $100,000 to Victorian Labor in Sept 2006 just before signing of Kew Cottages contract
• Has used politically connected lobbyists and consultants including former Labor senator Graham "Richo" Richardson and Victorian Liberal powerbroker and ex-Places Victoria chairman, Peter Clarke

Lack of clarity about costs, profits and government returns highlights the poor public accounting for the scheme by both Major Projects Victoria and the client department, Human Services, a problem noted by in the past by both the state Ombudsman Victoria and the Auditor-General.

The failure to clearly, publicly report detail of the Kew project seems at odds with the spirit of "open-book" accounting - where the government has access to its private partner's books - and which is meant to apply in the case of the Kew project.

In response to questions, a Major Projects spokesman said the agency were afforded "full transparency" on Walker's costs and profits and was satisfied with them. "MPV takes independent quantity surveying and other advice to verify KDC's project expenditure." Major Projects refused to release such detail.

Walker Corporation did not answer detailed questions, but issued a short, unattributed statement noting the company's pride in its "sensitive relocation of the 100 severely handicapped Victorian residents who now live in beautiful parkside homes".

The Andrews government has also refused to open the books.

Major Projects minister Jacinta Allan did not answer a list of written questions. Instead, she issued a brief statement in which she stressed that the government would "use the experience of the Kew Cottages development to improve the delivery of future projects".

From the outset the government's partnership with Walker, who was announced as preferred bidder in mid-2005, was controversial. More than a year after the announcement, negotiations with Major Projects bogged down and with a state election looming, Walker tipped $100,000 into ALP coffers, the company's first gift to Victorian Labor since 2000.

A contract was signed on the last day before the caretaker period ahead of the state election that year. In 2007, The Age also revealed intervention in the Kew scheme by NSW Labor-right heavy-turned lobbyist and Walker associate, Graham "Richo" Richardson.

Through the Bracks years the Coalition opposition declared the Kew deal was dodgy, vowed to scrap it and, later, to make Kew the first investigation by its promised anti-corruption commission, IBAC.

But after winning power in 2010 the Liberals went quiet, the silence coinciding with big Walker donations to the Liberal party.

The Baillieu government abandoned the idea of the IBAC probe and, in 2014, struck a deal with Mr Walker to scrap plans for facilities for residents with disabilities in three remaining heritage buildings, including a hydrotherapy pool, in return for a cash payment from Walker.

The then Liberal government, without protest from Labor, claimed the facilities were "potentially unviable", saying they duplicated existing services elsewhere in Kew. The three remaining heritage buildings at Kew are now fenced-off ruins for sale on the open market.

Max Jackson has had a longstanding interest in the Kew site, including through a 17-year stint as chief executive of the Kew Cottages complex which the Kennett government closed to new admissions in the late 1990s.

"This government has an opportunity to rectify a lack of transparency by successive governments and ministers," Jackson said.

He called on the Andrews government to "come clean".

*An estimate based on the $86.5 million budget from the early 2000s which did not include other costs of managing the project across government since

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