About 24,000 commercial properties in London that could be turned into temporary housing or workspaces are lying empty, a report has found.
Research from Centre for London discovered the floor space of unused buildings amounted to about 1.8 million sq m (2,700 hectares) of land.
The think tank said temporary schemes like Boxparks and gardens had proven popular but there was space for more.
It has called for more flexibility to set up "meanwhile projects."
More than 20,000 commercial properties in the capital have been empty for at least six months, with 11,000 of those vacant for two years, according to Centre for London.
The think tank said space of that kind could be used for schemes such as temporary housing, charity works or retail units.