Green Belt extension appeal wins because permitted development fallback would be worse

A Green Belt extension appeal in Guildford has been allowed after an Inspector found that the owners could use permitted development rights to build a fallback scheme with a marginally greater effect on openness.

The proposal at The Cottage, Blanket Mill Farm, Worplesdon, was accepted by both parties as inappropriate development because the first-floor and rear extensions would amount to a disproportionate increase over the original building. That meant substantial Green Belt harm had to be weighed against other considerations.

The decisive factor was not a claim that the appeal scheme caused no harm. Inspector G Ellis found a loss of openness. But a combination of prior approvals and permitted development rights gave the owners a realistic fallback which would produce the same footprint and a taller, less coherent building.

Green Belt extension appeal began with acknowledged harm

The Green Belt extension appeal, reference 6012736, concerned a first-floor extension, single-storey rear extension and associated alterations to an H-shaped bungalow in a small enclave of homes at the end of an unmade lane.

The property lies in the Green Belt. The scale of the proposed additions meant that the development did not fall within the Green Belt exception for extensions that are not disproportionate additions over and above the size of the original building.

The Inspector therefore treated the development as inappropriate. Under national Green Belt policy, inappropriate development is harmful by definition and substantial weight must be given to that harm.

There was also a real effect on openness. The proposal would enlarge the footprint, add depth to the rear and create a first floor across most of the building. That would increase both its spatial presence and its visual mass.

However, the harm was localised. The building sits well back, the extensions would not be readily seen except from neighbouring properties and the resulting house would not be out of scale with its plot or the surrounding enclave.

That left the Inspector with limited but genuine openness harm, on top of the definitional harm arising from inappropriate development.

Prior approvals created a credible fallback

In the Green Belt extension appeal, the owners relied on a package of permitted development works as a fallback. That included upward extensions and a large single-storey rear extension supported by earlier prior approval decisions.

Importantly, a fresh Class AA prior approval had been determined while the appeal was under consideration. Guildford had advised that prior approval was not required for an additional storey. The Inspector invited comments from the Council and then took that decision into account.

This strengthened the fallback considerably. It was no longer just an abstract suggestion that permitted development rights might be used one day. The Council itself acknowledged that there was more than a theoretical prospect of the works being carried out.

That is the essential threshold for a fallback argument. Planning decisions do not normally give meaningful weight to speculative alternatives. There needs to be a real prospect that the fallback could and would be implemented if permission for the preferred scheme were refused.

Planning Geek’s guide to Green Belt planning explains the special policy tests that apply to extensions and other forms of inappropriate development.

The fallback was slightly more harmful

In the Green Belt extension appeal, the appeal scheme and the permitted development fallback would produce the same footprint, but their form and appearance differed.

The fallback would create a taller building, particularly on the eastern section, with the walls of the main building raised directly and a higher roof above. By contrast, the appeal design used a lower ridge line, dormers serving the first floor and a form the Inspector regarded as more coherent and integrated.

There were no comparative floor-area or volume calculations before the Inspector. That did not prevent the fallback being weighed. The visual and spatial differences could still be judged from the plans and the authorised permitted development works.

Inspector Ellis concluded that the fallback would have a marginally greater effect on Green Belt openness. She gave that prospect significant weight.

That finding is the key to the appeal. The planning system was not choosing between the appeal scheme and leaving the existing bungalow untouched. On the evidence, the realistic alternative was a permitted development scheme which would itself enlarge the building and would do so in a slightly more harmful form.

Fallback tipped the very special circumstances balance

In deciding the Green Belt extension appeal, the Inspector still gave substantial weight to Green Belt harm. The appeal scheme remained inappropriate development and there would be a localised loss of openness.

But the more harmful fallback was an “other consideration” of significant weight. In the particular circumstances, it clearly outweighed the substantial Green Belt harm.

The Inspector therefore found the very special circumstances needed to justify the development.

This is a useful reminder that a fallback can affect the Green Belt balance even where the appeal proposal itself falls outside the normal extension exception. The relevant question is not whether permitted development rights make the appeal proposal lawful. They do not. The question is what would realistically happen if permission were withheld, and whether that changes the planning consequences of refusing the preferred design.

Flood risk and bats were dealt with separately

The appeal also involved two technical matters which were not allowed to derail the main planning balance.

A flood-risk condition requires the development to follow the submitted Flood Risk Assessment, including a minimum finished floor level 150mm above ground and no storage or works within eight metres of the watercourse.

Bat surveys had also identified the need for mitigation. The Inspector considered the Habitats Regulations duty and was satisfied that the submitted measures, secured by condition, would avoid significant harm to protected species and their roosts.

She did not attempt to duplicate Natural England’s separate licensing role. Instead, the planning decision proceeded on the basis that the other regulatory regime would operate effectively, subject to the evidence and mitigation before her.

Why the decision matters

For householders and advisers, the Green Belt extension appeal is a strong example of how a permitted development fallback should be assembled.

It was supported by actual prior approval decisions, including a recent Class AA decision covering the additional storey. The fallback was sufficiently defined for the Inspector to compare its footprint, height, massing and appearance with the appeal scheme.

It also shows why a better-designed planning application can sometimes be preferable to piecemeal permitted development. Here, the appeal scheme remained inappropriate Green Belt development, yet its overall form was more coherent and its effect on openness was marginally less harmful than the realistic lawful alternative.

The decision does not mean every permitted development fallback will establish very special circumstances. Weight depends on whether the fallback is genuinely available, whether there is a real prospect of implementation and how its planning effects compare with the proposal actually before the authority or Inspector.

Where those elements are present, however, refusing the better scheme can become difficult to justify simply because the policy starting point is restrictive.

Appeal details

Appeal: 6012736
Site: The Cottage, Blanket Mill Farm, Goose Rye Road, Worplesdon, Guildford
Application: 25/P/00976
Inspector: G Ellis BSc (Hons) MSc MRTPI
Decision: Allowed, 5th October 2026

The full decision was reviewed via AppealBase.