The case of Cheshire East today is an interesting one as they claim they should only have a 5% buffer not 20% as tow of its constituent authorities had a housing monirotium imposed by the RSS and so they cannot be blamed. Two problems:
1) Appeals have consistently held that the 20% provision is not designed to be punitive, that is because of the wording in NPPF para. 47 that it is to ‘to provide a realistic prospect of achieving the planned supply’ i.e. to make dmaned sure you return to trajectory when below it. Blame is not a material consideration here.
2) It is within para. 47 of the NPPF which makes clear the measurement of ‘needs for market and affordable housing in the housing market area’ so if there is persistent underdelivery across the HMA as a whole then the 20% rule applies to all applications in that HMA, a view reinforced by 1) it is not about blame but about delivery. There is nothing in para. 47 that implies measurement fo need and delivery occur across different geographic areas, that would be crazy.