Around two-fifths (41%) of lock-up garages owned by councils across the capital are empty or in disrepair, according to the findings from property crowdfunding website Property Partner.
Researchers submitted freedom of information (FOI) requests to 32 London boroughs, and the findings were made from 24 complete responses received.
Out of the 53,640 council-owned lock-up garages in the survey, 22,230, or 41%, were found to be standing empty for various reasons. In some boroughs, nearly three-quarters of garages were not in use, the research found.
Property Partner also asked councils to disclose the average size of their garages.
It calculated that the total stock of garages, including those both in use and vacant, could provide enough square footage for at least 16,000 new homes.
Dan Gandesha, chief executive of Property Partner, suggested the "shapshot" figures show there could be wider opportunities to develop publicly owned land that is being underused, such as that in the health sector.
He said: "If a significant number of council garages, which are part of housing estates, are not even rented to those who should have a right to them - local authority tenants - then it could be argued that this is a wasted opportunity."
Looking across the boroughs, the survey found that nearly three-quarters (74%) of garages in Ealing were empty, the highest proportion among the boroughs which gave complete responses.
A spokesman for Ealing Council said: "A large number of our garages are too small for modern cars and people no longer want to rent them.
"As a result, we are redeveloping them to provide new housing where this is feasible."
He said 300 new homes are being built on garage sites across the borough and added: "Many of the empty garages are on estates which are being demolished and rebuilt.
"As they become vacant they are not re-let and will be demolished as part of the wider scheme, which will use the land they occupy to help create more homes."
Sir Steve Bullock, London Councils' executive member for housing, said: "Many councils are converting garages and other small infill sites on existing council land where it is possible to make them fit for habitation.
"But in many cases such sites are unsuitable for development or on land earmarked for large-scale future development.
"There is no quick fix for London's housing crisis.
"Boroughs are doing their part by granting planning applications for tens of thousands of homes every year but, as we have made clear, they must be given the support and resources to ensure tens of thousands more, of a range of tenures, can be built."