I'm not sure if the situation in Britain is the same as it is in the States, and would love to be corrected if I'm wrong. In the U.S., a lot of the empty real estate properties exist because the owner gets a tax right-off for owning vacant properties. Indeed, for years the office building next to my work was empty, and was serving as a massive tax right-off for some dentist in New York. Because he had no real interest in selling, he kept the asking price to rent/sell insanely high because having tenants wasn't the point. He also didn't seem to care that keeping the building vacant was torpedoing the local property value.
If Britain has the same situation, then instead of seizing private property from their legal owners, how about instead removing the tax breaks, which would discourage the vast ownership of vacant properties.
I am not an expert.
However I believe that in the UK tax right offs are permitted for relevant costs, losses and government favoured activities,
and not simply for owning empty properties.
There is no local council tax for properties if they are unfurnished and unoccupied.
This concession was designed to protect builders and renovators with unsold and unrented property, but it is misused by speculators.
In the UK the problem is that a lot of rich foreigners buy up property and then sit and watch property price inflation double their money.
Many London (and also Manchester) properties are sold to Chinese or Arabic purchasers who have never even seen them.
In theory they should pay capital gains tax on such profits, but there are an awful lot of tax avoidance/evasion scams.
For instance, the property is bought in the name of an overseas company; the owner sells the company or its (obfuscated
via tax havens), parent company and not the property itself, so the claim is that there is no change of ownership and no tax due!
In theory the UK should benefit from such elevated building activity, but as much of the workforce are temporary immigrants
and off book, the benefits to central government and local councils are very questionable.