Burnham has already delayed the draft NPPF He needs to get it published and resist fiddling and weakening the draft, as well as supporting other proposals coming through eg medium sites. No path to building hundreds of thousands of council homes without a system enabling millions of private homes.
Paul Cheshire (LSE, CEP) warns that radical reform of the planning system will be needed if the latest housebuilding pledge is to be met. https://blogs.lse.ac.uk/politicsandpolicy/without-radical-planning-reform-burnham-cannot-build-the-houses-hes-promising/