When it comes to housing, saving special places means we have to build the right homes in the right places, a familiar theme of this blog. That’s what the planning system is meant to help us do.

The national problem is that we’re not building enough homes, and some areas are not consistently building enough.

But how do you work out how many homes are needed in a place?

Planners have to take a number of factors into account, including population and household growth, economic growth, migration and the types of new homes needed.

Once you’ve agreed what the local need is, the final figure in the plan (the target or requirement) could be more or less than the need – neighbouring areas might agree, for example, that if one area is heavily constrained, it might be better to build the homes in a less constrained area.

Arguing about the numbers takes up a lot of time at local plan inquiries.

If everyone used the same accepted approach to working out the need, that would save time and money and let planners focus on other important things, like the quality of the places we build. There’s a certain logic to that argument.

So the Government has proposed a standard approach, which builds a measure of affordability into the need number. The least affordable places (generally in the South East of England) get a higher number, because building more homes here should make them more affordable – it’s a matter of supply and demand, at least in theory.

The problem is that introducing a strong affordability measure into the definition of need has implications for the environment.

The map below shows the change between housing need under the new method compared with the current assessment, for each local authority. It’s based on figures from the Department of Communities and Local Government (DCLG).

There’s a clear bias of reds (increased housing need) in southern England, and greens (reduced housing need) in the north, roughly on an axis from the Severn to the Wash.

But what if the areas of increased housing need were also areas of high environmental quality?

The second map shows how local authorities are constrained by environmental factors. Again, it’s based on DCLG’s own figures. It comes with a lot of caveats – some constraints aren’t shown, eg flood risk; it tends to bias the picture towards landscape-scale designations like the Green Belt, National Parks and Areas of Outstanding Natural Beauty (AONB) rather than more specific features like Sites of Special Scientific Interest (some of which are designated under the EU Nature Directives, or as internationally important Ramsar sites).

The area of constraints also doesn’t include buffer zones around protected areas, which are important in places like the Thames Basin Heaths to minimise the indirect impact of development, for example through increased recreational pressure.

Local authorities in green have a lower proportion of environmentally constrained land but may still cover some very significant places for wildlife – the coast of East Anglia, with its many RSPB reserves, is a good example, and also authorities like Medway in Kent, which includes the Lodge Hill and Northward Hill SSSIs as well as coastal protected areas. We also need to remember that locally-designated or undesignated land such as urban greenspace can be important for nature as well and provides people with opportunities to access nature. However in the green areas on the map there is all the more reason to direct development away from the most important protected sites.

So it’s a crude measure of constraint; indeed to be frank it’s an inadequate measure for sensible planning, but even on its own terms it shows there’s a potential problem: higher housing numbers have implications for the natural environment.

Looking at southern England, there’s a clear ring of increased need in constrained areas around London – this is the impact of the Metropolitan Green Belt, but also the Chilterns AONB and nature conservation sites such as the Thames Basin Heaths Special Protection Area (SPA).

You can see other overlaps of increased need and high constraint on the south coast: for example in East Dorset (a combination of AONB, Green Belt and the Dorset Heathlands SPA) and in East Sussex (AONB).

In northern England, York stands out as an area of increased need and high constraint, which is mostly due to the York Green Belt.

Where these maps intersect – areas of increased need and high constraint - also tend to be desirable places to live. They enjoy a good quality environment near to economic opportunities, mostly in the south east. It’s no surprise then that they are less affordable.

The question is – over the long term, are they really the places we want to keep building?

Working out the numbers for each local authority in isolation isn’t really enough for the scale of challenge we face – both the housing challenge and the environmental challenge. Proper strategic planning would direct growth to less constrained areas of demand.

The RSPB calls on the Government to commission a housing and environmental study for the whole of the wider south east; ideally everywhere below that line from the Severn to the Wash, but certainly for the ‘greater south east’ of London and the surrounding counties. It should examine all the environmental constraints and the opportunities for environmental enhancements from new development – including more, bigger, better and joined up protected areas. It’s important to take a long-term, reflective look at the future of our land, establishing where the natural environment is already close to or exceeding its capacity for development. What we need is a set of strategic policy options for meeting development needs in harmony with nature, which complements the 25 Year Plan for the Environment already in preparation.

The South East desperately needs better strategic planning. But at least a study like this would lead to much more informed decisions on every local plan, that stop us building more homes that destroy the best places for nature.

What do you think?