[Mindwipe]

Yeah, that is certainly the reasoning that pushing prices up is based on in London.

Another angle is that more expensive properties are more efficient, so the bubble of foreign investment in property has lead to a rise in the construction of hyper-premium properties which the market does not especially demand, and a lack of construction of mid-range or lower tier housing, pushing the prices up in those sectors.

[YorkshireSeason]

   rise in the construction of hyper-premium 
   properties which the market does not 
   especially demand,

If you look at the parts of London with extreme building activity over the last few years (Nine Elms, Battersea Power Stn, Docklands, Aldgate, Old Street, Stratford, Kings X), you'll find that almost everything falls into the studio, 1-bedroom or 2-bedroom range. There has also been a lot of development of commercial student accomodations, see e.g. [1]. Pretty much the antithesis of "leaving things empty".

[1] https://www.theguardian.com/education/2018/may/27/revealed-d...