I don't know how to link from my phone but the report is featured on the BBC News website.
Basically, the poor and disadvantaged/well off divide, academically speaking, is greater compared to Hong Kong, Japan, Finland and a few others..
No doubt the usual suspects will use this report to bash the 11+ GS system. and/or the private system. These schools account for a relatively small proportion of the UK school population so one can hardly blame our problems on selective education. So what else? Are the UK poor not as clever as the poor in other countries or are they less aspirational or is there some other reason for our low ranking?