The NAO's report (52 page / 501KB PDF) said that although the percentage of major residential applications determined on time had improved, this might reflect a greater use of agreed extensions to timescales rather than increased efficiency - and noted that the measurements did not include time spent on pre-application work.
The report also said that resourcing at all levels was a major issue in delivering new homes. The NAO said total spending by local authorities on planning functions fell 14.6% in real terms between 2010/11 and 2017/18, while core funding had fallen 37.9% per cent in the same time period.
Staffing was also identified as a problem, reporting that the number of local authority planning staff fell by 15% between 2006 and 2016.
Planning expert Nicholle Kingsley of Pinsent Masons, the law firm behind Out-Law.com, said: "This confirms what everyone involved in planning knows and has been saying for a while now: the lack of resources at all levels is a direct contributor to the delay in the delivery of houses."
The report noted that there were delays with the Planning Inspectorate as well as local authorities. The time the inspectorate was taking to determine housing appeals had risen significantly between 2013/14 and 2017/18, despite a fall in the number of appeals.
It also said the inspectorate was failing to meet many of its statutory targets and had seen a fall in staff numbers by 13% between 2010 and 2018.
Infrastructure and planning expert Robbie Owen of Pinsent Masons said: "This should not be seen as an opportunity to criticise the Planning Inspectorate but rather to recognise that they are also severely under-resourced. The NAO report itself recognises that the housing ministry 'does not understand the extent of skills shortages in planning'."
"It is clearly now time to have a meaningful national debate on the role and status of planning professionals in central and local government and in the Planning Inspectorate. Their role and value has steadily been eroded and downgraded over the years such that we no longer attract, train, develop, reward and sustain enough people with the right skills, depth and breadth of knowledge and understanding as well as core aptitude," Owen said.
The Royal Town Planning Institute said it welcomed the NAO report but last week released its own report (52 page / 2.3MB PDF) finding that under-resourcing in local authorities, coupled with government reforms, had led to a climate of "reluctant outsourcing" which meant planning had become a regulatory, reactive function for many.
Housing expert Iain Gilbey of Pinsent Masons said the NAO report added "another significant voice to the existing chorus of demand for more central government resources for the planning system", an issue which had been raised by the House of Commons Housing, Communities and Local Government Committee in a report on land value capture and by attendees at a recent event hosted by Pinsent Masons and Grant Thornton on housing delivery.
"If the government continues to put the delivery of housing at the centre of its domestic policy agenda, then it must match that rhetoric with increased funding for and sustained investment in the planning system, at government and local authority level as well as at the Planning Inspectorate. Uncertainty and planning delay act as disincentives to investment and delivery, both of which must be avoided at this time," Gilbey said.
The report said the National Planning Policy Framework, published in July 2018, was an important step in planning policy but it was too early to tell whether the changes it introduced would be effective.
The NAO added that the way housing infrastructure was funded lacked "cohesion and certainty" and involved a number of different government departments as well as the private sector. It found that the system to get developers to contribute funding towards the cost of infrastructure was not working effectively.
The report added that: "The Ministry of Housing, Communities and Local Government has little oversight of how local authorities generate income from planning. It does not collect information on the extent of planning performance agreements, or how much income they are generating."