Members of the public who have ever looked at a rather forlorn building and hankered after buying it can find out if it is in government hands through a website launched on Wednesday by the Cabinet Office – and make a case for it to be sold on the open market.

About 31,000 publicly owned assets are listed on the site, which has been launched to support a drive to encourage individuals and organisations to challenge central and local government about underused property and land. Under a right to contest introduced in January, anyone can force the government to explain why a building or plot is not being used fully. If the department that owns it cannot justify its current use, it will be forced to release it for sale.

The online Government Property Finder lists all centrally owned buildings and land, which can be searched by location, so consumers can track down sites in their neighbourhood. The results include those that have already been earmarked for sale or for rent.

Although the Cabinet Office’s announcement includes the assurance that “historic assets such as Downing Street or the Treasury building won’t be sold off” – even if some might argue that they could be put to better use – some of the more than 500 properties listed are landmarks.

Among them are the Grade II listed Old War Office Building in Whitehall, which the Ministry of Defence announced it would be selling last year, Bidston observatory in Wirral, which was built in 1866 and is owned by the Natural Environment Research Council, and the airfield at RAF Wyton in Cambridgeshire. The airfield was the base for the first RAF sortie of the second world war but its closure was announced last year.

Several prisons closed by the Ministry of Justice are also included, including HMP Shepton Mallet in Somerset, which was Britain’s oldest working prison and housed the Krays after the war.

Central government owns almost £350bn worth of land and property around the country. Estimates suggest that up to 40% of land suitable for development and about 27% of brownfield sites suitable for housing are owned by the public sector and, with the property market at crisis point, the government is keen to be seen to be releasing unused plots. Since 2010, it has made available land for 62,000 homes and it has set a target of 100,000 homes by 2015.

Recent research by the property firm Knight Frank found that the country’s biggest housebuilders and developers believed improving access to public sector land was the biggest additional step the government could take to improve housing delivery.

The minister for the Cabinet Office, Francis Maude, said: “As part of our long-term plan for a stronger economy we are slashing our own costs and getting the most out of the property we own.

“Since the 2010 general election we have got out of 1,250 properties, but we need to do more. We want the public to use this new map and the right to contest to challenge us to release properties we are not using efficiently enough to cut the deficit, support growth and provide more houses.”

Alex Dawson, head of public sector consultancy at property company Savills, said developers had shown an interest in the right to contest but he had not yet handled any applications.

“I think this tool is more likely to help individuals and small organisations who will find it useful to be able to identify ownership of property and land,” he said. “There are some organisations in the public sector that operate more slowly than others. If this speeds things up it is a good thing.”