Also, coming from anybody hand-wringing over the abstract ideological implications of this proposal in the face of the human suffering it's meant to address, I'm never going to take insinuations about left-wing ideas being "great in theory, but..." or utopian exercises divorced from reality seriously ever again.
This, also it needs to be pointed out just how disgraceful the housing situation in London actually is - these empty homes are, in many ways, empty boxes that are owned by Russian billionaires as a means of money laundering. And they have contributed to the insanity that is London housing these days, where people on low, or even medium incomes, are forced into the kind of crap quality, unsafe housing of the likes of Greenfell tower.