The Grey Belt is a crucial opportunity for expansion

Since stepping into Number 10 last year, the Labour government has made its intention to build 1.5 million new homes clear. It has not been shy about cutting ‘red tape’ that they claim slows down planning and development, announcing a stream of changes and reforms. It has recently announced the Planning and Infrastructure Bill, and reintroduced mandatory housing targets for councils through the revised National Planning Policy Framework (NPPF).  

It was in this revised NPPF that the term ‘grey belt’ was first introduced. Grey belt is previously developed land, and/or land which doesn’t contribute strongly to green belt purposes. Using grey belt areas for development could be an important part of achieving the government’s 1.5 million new homes target. However, plans for grey belts in the NPFF sparked debate and widespread calls for clearer guidance. Further clarification in the Planning Practice Guidance (PPG) published in February 2025 was therefore welcomed, including practical detail on how to identify grey belts.  

What will it achieve?

In the Spring Budget, it was announced that grey belts, along with other planning reforms, would help boost GDP 0.2 per cent by 2029-30, an added extra £6.8bn to the UK economy.

It remains to be seen how effective the grey belt will be in boosting economic growth and achieving housebuilding targets. However, done right, the identification of grey belt areas will provide evidence for authorities seeking to rapidly unlock unsuccessful green belt land, providing much needed affordable homes, jobs and community infrastructure.

The challenges

Green belts were introduced in 1947 to protect the countryside from urban sprawl by keeping land permanently open. While there may be benefits to grey belt development, we must also be confident that development in these sites will not undermine the important role of the green belt.

As a new policy area, the process for identifying grey belt is still being tested. The new PPG seeks to provide a consistent framework for the assessment of green belt areas and dictate whether the land constitutes grey belt – preventing the unrestricted sprawl of built-up areas, preventing neighbouring towns from merging and preserving the setting and special character of historic towns. The guidance clarifies definitions of key terms, such as ‘large, built-up areas’ and ‘towns,’  and provides guidance on the appropriate scale of areas to be assessed.

Crucially, the definition of grey belt excludes land such as National Landscapes, National Parks, Sites of Special Scientific Interest, Local Green Spaces, irreplaceable habitats and heritage assets. The guidance clarifies this approach – importantly noting that in some cases it may only be possible to provisionally identify grey belt areas before a detailed proposal has been developed.

Grey belt thus provides an opportunity to increase the amount of land available for development whilst protecting the strongest performing areas of green belt and those areas subject to major constraints. There are now several planning applications which have been approved on grey belt land. 

Next steps for councils

The government believes that development plans should be made at the local level to ensure that development serves the needs of communities. Despite this, the government recently confirmed that less than a third of councils have up-to-date local plans, which can lead to speculative and unplanned development. While there are many reasons for this, the complicated and lengthy planning process is a significant factor.

The government is rolling out reforms to help councils streamline the process, aiming to achieve universal coverage of local plans. Through this, councils must update their green belt evidence, supporting the identification and potential allocation of their grey belt land. Councils might be able to use existing green belt reviews rather than starting from scratch, subject to four key considerations:

1. Has a strategic and more spatially refined study been completed?

2. Is the methodology consistent with the NPPF / PPG broadly?

3. Has assessment against all purposes been undertaken?

4. Have there been any significant on the ground changes that might alter performance scores?

Our initial work suggests that assessment approaches remain broadly appropriate. However, the main sticking point is around the interpretation of ‘towns’, which requires a refresh of individual assessments in some instances.

Green belt reviews are time intensive, so it’s important to be pragmatic about the assessment area – for example, by focusing on assessing sites that are most likely to be deliverable.

With the arrival of the Planning and Infrastructure Bill, attention will also need to turn to the assessment of green belt at a more strategic level to feed into Spatial Development Strategies.

The role of private sector

Recent planning reforms provide a once in a generation opportunity to speed up  processes so that decision making is plan-led. As part of plan-making, local authorities must take a fresh look at the green belt to identify areas which are not highly performing and could instead be allocated for new development.

The private sector needs to work collaboratively with the public sector to bring forward development in the most sustainable locations, making the most of grey belt land. Through cross-sector collaboration, we can build and expand towns and cities with effective, affordable housing, while preserving the original purposes of the green belt.

Chloe Salisbury, director of town planning, Arup