Market Size
The UK’s housing stock is worth £5.75 trillion, 40% larger than the total market cap of UK shares listed on the London Stock Exchange. The private rented sector (PRS) equates to £1.2 trillion, or 1.3 times the size of the entire UK commercial property market.

UK PRS – European Comparison
The chart below shows the UK PRS sector compared to other European countries. It shows that Switzerland and Germany have a disproportionately large PRS sector when compared with the rest of the former eastern block / communist states. Slovenia, Hungary, Slovakia, Romania, Bulgaria and Estonia all have an extremely small PRS sector as a legacy of the state ownership of property assets.
Ignoring these outliers, the UK PRS at 18.5% is close to the average for Europe at 16.0%.
Interestingly out of 11 countries studied by London School of Economics and the University of Cambridge, the UK was the only country to show continued growth within the PRS sector.
Sources:
http://www.londonstockexchange.com/statistics/home/statistics.htm
http://www.dmo.gov.uk/index.aspx?page=Gilts/Portfolio_Statistics
http://pdf.savills.com/documents/Total%20Value%20by%20Tenure.pdf
http://www.bpf.org.uk/about-real-estate
http://www.lse.ac.uk/geographyAndEnvironment/research/london/pdf/The-Private-Rented-Sector-WEB[1].pdf
www.communities.gov.uk/documents/housing/xls/table-104.xls