Marrons has published its Green Belt Report, supported by the Land, Planning and Development Federation (LPDF).
The report found that the introduction of grey belt policy in the revised National Planning Policy Framework (NPPF) in December 2024 has already had a noticeable effect on planning decisions.
In 2025, for the first time, more grey belt planning appeals have been allowed than dismissed.
Overall, 57% of grey belt planning appeals were allowed (74 out of 129), between December 2024 and August 2025.
Among residential schemes, 55% were allowed (34 out of 62), while major residential schemes for 10 or more dwellings had an 80% success rate (16 out of 20).
Applications from LPDF members went up by more than 160% between January and June 2025 compared to the previous six months.
Residential schemes accounted for 73% of all grey belt appeals.
The remainder included commercial at 10%, industrial at 9%, sui generis at 6%, retail at 1% and leisure at 1%.
For non-residential grey belt appeals, 53% were allowed.
Of all residential grey belt planning appeals, 55% were allowed.
There were 20 major residential grey belt planning appeals (for 10 or more dwellings) and 80% of these were allowed.
Of the 43 minor residential grey belt planning appeals, 45% were allowed.
The average size of a residential grey belt planning appeal was around 30 dwellings, with the most common size being one dwelling.
Most housing proposals at appeal were relatively small.
For major residential grey belt appeals, the average size was over 100 dwellings, with a total of 1,620 dwellings.
The South East accounted for 52% of all grey belt appeals, with the East at 17% and the West Midlands at 12%.
Most appeals were for smaller schemes, but the largest were for over 100 dwellings.
Between December 2024 and August 2025, there were 20 major residential grey belt planning appeals decided, of which only four were dismissed, giving an 80% success rate.
Nicole Burnett, senior policy and research manager at the LPDF, said: “We welcome the publication of this important research by Marrons, which highlights the positive and practical impact grey belt policy is already having on planning and housing delivery.
“The analysis provides clear evidence that more flexible approaches to land designation can unlock sustainable development in the right locations.
“However, while this is a step in the right direction, the government must go further – and act quickly – to deliver the wider planning reforms and fiscal incentives needed to tackle the housing crisis.”
Roland Brass, planning director at Marrons, said: “The data is clear – grey belt is a gamechanger.
“An 80% success rate for major residential appeals is unprecedented in the Green Belt context.
“The grey belt policy has not only opened up a new much-needed supply of land to help contribute towards addressing the housing crisis but it’s also giving developers and local authorities a more objective framework to work within.”
Brass added: “We’re already seeing the Planning Inspectorate, planning committees and officers becoming more confident in identifying and consenting grey belt schemes, which helps accelerate delivery in the coming years.
“The fact that more than half of non-residential appeals are also being allowed demonstrates grey belt is not just unlocking opportunities for housing, but also for employment, commercial and community, infrastructure and energy uses.
“Grey belt policy has helped make the planning system faster, simpler and more certain, which is positive for all parties involved.”
He said: “The more objective approach towards the assessment of Green Belt land is massively welcomed.
“However, sites are still judged on a case by case so demonstrating a strong and evidenced grey belt case is crucial.
“It is important to remember that grey belt provides the window of opportunity but sites must still be sustainable and proposals still need to deliver benefits.”
He added: “Through the mandatory delivery of increased affordable housing, new infrastructure and accessible open space, new schemes are delivering benefits across the country while ensuring the vast majority and best parts of the Green Belt are protected.”
