That number could do with more details on how that number was counted. Apart from provisional permission (which still a lot of further planning effort), I know

That number could do with more details on how that number was counted. Apart from provisional permission (which still a lot of further planning effort), I know from bitter experience that a "granted" full permission does not actually mean you can build there yet. It's also possible for duplicate grants where only one of the permitted options can actually be built. It would need to count the number of houses which have been granted full permission and for which all pre-commencement conditions have been discharged. (Also, if the article is right and the number of applications has been increasing over time, it could well be that the majority of the not-(yet)-built houses are in the more recent batch).