A move away from public control would affect homebuyers' confidence, says Public and Commercial Services union
The 150-year-old Land Registry could be part-privatised under government plans condemned by union leaders as hugely risky.
As the Treasury seeks £10bn of extra privatisations, Michael Fallon, a business minister, unveiled a series of options for the body, which is the UK's comprehensive source of data on house prices and employs around 4,500 civil servants.
These include turning the Land Registry into a joint venture between the state and a private company, or letting a private firm run it as a government-owned organisation.
The Public and Commercial Services (PCS) union said turning it into a government company is inevitably the first step towards full privatisation, as happened with the Forensic Science Service.
It said any move away from public control would put at risk the confidence that homebuyers have in the service, which charges fees for certain checks on who owns land.
The union also raised worries about the Land Registry's ability to guard against fraud if a range of private firms are involved in maintaining the register and the potential increased cost to homebuyers if it is run for profit rather than in the public interest.
"There is absolutely no evidence that this would improve services at what is a well-respected and trusted 150-year-old institution, and senior managers have so far failed to make a coherent case," said Mark Serwotka, general secretary of the PCS.
"Any perceived benefits in taking what is inevitably the first step towards privatising the Land Registry are overwhelmingly outweighed by the huge risks involved."
Announcing an eight-week consultation into its future, Fallon said: "Giving Land Registry more flexibility to operate in the modern world will enable them to become a leader in digitising land and property services and support economic growth in the wider economy. We welcome views from all interested stakeholders to help us shape the future of land registration services."
It comes after Danny Alexander, the chief secretary to the Treasury, announced he has doubled the coalition's target for the disposal of state assets to £20bn over the next six years, and follows the government's controversial flotation of Royal Mail last year.
As part of an extra £10bn of privatisations, Britain's stake in the cross-channel rail operator Eurostar will be sold off.
A spokesman for the Department for Business, Innovation and Skills said full privatisation of the Land Registry is not being considered at this stage. Several years ago, a report by the Adam Smith Institute identified the Land Registry as a potential asset of interest to private equity companies.