Yeah you may be right, however I was under the impression that London in particular was infested with overseas investors, buying up as many houses as they could and then letting them out at inflated rents, thus pushing up the value of other properties when they come on the market.
Well, I can add a data point to that. The ground floor maisonette below us has had three owners since the rather nice old duffer, Graham, who lived there when we first moved in 'upstairs'. Sadly he died of a massive heart attack one Sunday while there on his own; I had to help the police break in after they got a "welfare check" call from one of his friends who he has supposed to visit that day.
The next couple to buy it lived there for a couple of years, then moved and rented it out, citing the difficulty of selling it. It then had a succession of tenants for a few years. The pattern then repeated itself with another couple living there (couple of gay lads for what it's worth) who also lived there a couple of years, needed to move, and rented it out to a nice Ukrainian lesbian couple for a few years, again citing difficulty in selling it. They finally sold it a few months back and the new owner hasn't moved in, hasn't let it, and so we don't yet know what the next chapter holds for it.
Our flat used to belong to Graham's sister, who had bought it from a gay couple who had owned it since the 60s, so our whole house has quite some LGBT history; I wonder if Stonewall ought to put up a pink plaque?
Anyway, I think that suggests that there's a lot more driving the rental market than rapacious commercial landlords buying stuff up and renting it out at exorbitant prices.