[holding answer 19 November 2007]: Communities and Local Government do not hold data on the percentage of gross national product spent on (a) housing and (b) affordable social housing in each of the OECD countries. There are data available on the percentage of gross domestic product spent on housing by OECD countries where data are available on the OECD website. Details can be found at:
http://stats.oecd.org/wbos/default.aspx?datasetcode=SOCX_AGG
There are a number of drop down menus on this page that allow you to select housing expenditure in both public or private sectors.