Sir Oliver Letwin has published his draft analysis of house building build out rates.

In the next phase of his work he is to consider, in the light of the build out rates analysis, what policies the government might adopt to ‘close the gap’ between permissions and homes completed on the largest sites and thus to increase the overall rate at which land allocated for housing is converted into new homes. Sir Oliver will present his recommendations to the Chancellor and the Housing Secretary at Budget time in the autumn.

See: https://www.gov.uk/government/news/ analysis-from-independent-review-into-buildinghomes-published