Policy G2 of the draft new London Plan says that the extension of the green belt "will be supported, where appropriate", adding that "its dedesignation will not be supported".
During a session earlier this week on the green belt and metropolitan open land as part of the plan’s examination at City Hall, the inspector asked for representations on whether the policy is "consistent with national policy".
In its response, industry body the Home Builders Federation said policy G2 "amounts to an unequivocal statement of opposition by the mayor to any release of the green belt under any circumstances".
Therefore, it said it was "contrary to national policy as expressed in both the NPPF 2012 and the NPPF 2018", given that both frameworks allow local authorities "to alter the green belt through local plans".
In contrast, the HBF said the current London Plan policy relating to the green belt "is consistent with national policy. It is consistent because it does not preclude the possibility of green belt release through a local plan or in ‘exceptional circumstances’ where this can help secure the objectives of the green belt".
In its response, business body London First said that, "in accordance with national planning guidance, and given the housing pressures London faces, there are likely to be exceptional circumstances where a borough should review its green belt boundary to meet its objectively assessed housing need or to deliver a better overall spatial strategy for London".
In these circumstances, London First said it "believes that the plan should not rule out a review of London’s green belt."
"Whilst the mayor has made a political commitment to protect the green belt, notwithstanding his political commitments to build more homes, the draft plan’s policy G2 is inconsistent with national policy as it makes no reference to ‘exceptional circumstances’ and, therefore, it is unsound", it said.
In its response, the London School of Economics said that policy G2 "sets up a crude blanket defence of green belt as a whole, counterposed with a view there is simply no need to draw upon it as a resource for housing, since a combination of brownfield re-use and intensification can accommodate the housing London needs".
It added that, "in its present form policy G2 is unacceptable because of the arbitrarily political way in which … spatial development strategies involving [London green belt] reform were excluded from consideration as a contributor to reducing the housing delivery gap".
But countryside campaign group the Campaign to Protect Rural England (CPRE) said that it "strongly supports" the new policy.
"Clarity and simplicity are key strengths of national green belt policy as set out in the National Planning Policy Framework (NPPF) and we are pleased that the draft plan retains and reinforces this clarity".
It added: "We believe policy G2 is consistent with national policy as set out in the NPPF which emphasises the permanence and openness of green belts."
A submission from the mayor of London also defended the policy. It said the 2012 NPPF, against which policies in the new London Plan are being assessed, "refers to green belt boundaries being altered only in exceptional circumstances and highlights the need to take account of sustainable patterns of development, including considering the consequences for sustainability of channelling development towards urban areas".
"This is consistent with the spatial strategy set out in the draft plan, which is focused on sustainable intensification of urban areas", it said.
According to consultancy Savills, which attended the examination session, the "balance of submissions was that the emerging policy of blanket protection for the green belt is not ‘sound’; specifically it is not consistent with national policy".
Nick de Lotbiniere, Savills head of London Planning, said: "There is a tension between the London boroughs’ ability to meet housing need and the constraints or lack of flexibility of the current green belt policy. The misalignment of London’s policy versus the national green belt policy has the potential to make the whole London plan unsound."
In July last year, housing secretary James Brokenshire criticised the emerging London Plan by saying its policies were "inconsistent" with national policy.
The draft plan was published in November 2017 and includes an overall housing target of 65,000 homes a year with much higher housing targets for the vast majority of London boroughs, compared to the existing London Plan.
A feature examining the most common "very special circumstances" used to justify green belt development can be found here.