One way of fixing it

Yesterday we had the unseemly sight of a landleech threatening to keep his houses empty in response to better tenancy laws. Meanwhile in Catalonia they have a solution for that: nationalisation:

Barcelona is deploying a new weapon in its quest to increase the city’s available rental housing: the power to force the sale of empty properties.

This week, the city’s housing department wrote to 14 companies that collectively own 194 empty apartments, warning that if they haven’t found a tenant within the next month, the city could take possession of these properties, with compensation at half their market value. These units would then be rented out by the city as public housing to lower-income tenants, while the companies in question could also face possible fines of between €90,000 and €900,000 ($103,000 and $1,003,000), according to Spanish news outlets.

That would certainly be one way of fixing the "ghost house" problem, and it would certainly incentivise landleeches to fill their properties. Even fines would be a start on that. Ultimately, we need a mass state house building program to increase supply and crush the market. But in the interim, measures like this may help ensure our housing stock is actually used as intended: as homes, rather than sources of tax-free capital gains.