Thanks, very interesting. I take the point made about leasehold flats data from @annaclarke.bsky.social but this research (showing 43% ex-council in PRS, if I understood correctly) and common sense - houses generally sold more than flats under RTB - does nothing to undermine the 40% figure.

Houses sold more than flats - but that doesn't mean that the same proportion of them end up in the PRS. We know that - generally - flats are much more likely than houses to be bought by landlords, so there's no reason to think this wouldn't be true for ex-RTB stock just as for other housing.