Even owner-occupiers may be "investors" - plenty of people's retirement plan involves selling their London home. But the houses are being lived in and are therefore providing real-world value, which is the main thing IMO - speculators can toss money back and forth all day, as long as the useful thing keeps happening.
Are they all owners or the owners actually "invested" in a piece of property calculating the rent passive income and the possible increase in market value as part of the overall rentability of their investment?