The number was around above 15% of households in 2002, however that number is likely to perhaps 20+% now.
It is the shear number of investors that flooded the market since the turn of the millennium that will cause the bubble to pop big time. More people are going to exposed to high leverage, depreciating assets and job losses.
"Finally, the survey shows that borrowing is an important source of finance for such investment. Indeed, investors are more likely to have loans on their properties than are owner-occupiers, and investment properties are typically more highly geared than owner-occupied properties...."
