How many investment properties is too many?

[Lilith7]

How though, do we get such a regime through a Parliament where property investors with multiple holdings are in the majority?

No one votes against their own interests. Ever. Especially politicians.

Well. I have some ideas. Any politician who owns, either in trust or as an individual more than say 2-3 properties should not get a vote on any law limiting property owning on the grounds that they cannot possibly be impartial.
And on the grounds that our housing situation - thanks largely to their (& that of other property owners) outright greed, is in dire straits & must be made fair as a priority. An urgent priority; as in within weeks.

Just damn well fix it.

Works for me.