Harrow BNG appeal ends with council ordered to pay full costs

The Harrow BNG appeal has ended with the Council ordered to pay the full costs of the proceedings after an Inspector allowed two new bungalows and concluded that Harrow had behaved unreasonably over both privacy and biodiversity net gain.

Appeal 6004526 concerned land at Eastcote Lane, Harrow, where outline permission was sought for two detached single-storey dwellings with accommodation in the roof space. London Borough of Harrow had refused the scheme over overlooking and BNG, but Inspector N Teasdale allowed the appeal on 30th September 2026.

The biodiversity findings are more nuanced than a simple “BNG can be fixed later” message. The Inspector agreed with Harrow that the correct baseline was historic grassland, not the gravel surface seen later, and also agreed that the proposed private-garden habitat gains could not simply be secured as claimed. The decisive question was whether the statutory biodiversity gain condition was nevertheless realistically capable of being discharged.

The BNG appeal still backed Harrow on the grassland baseline

The appeal site had once been grassland but was covered in gravel by the time of the Inspector’s site visit. That did not make gravel the correct starting point for the biodiversity calculation.

Harrow relied on aerial imagery from 2020 showing grassland. Inspector Teasdale agreed that the pre-development baseline should therefore be grassland and rejected the gravel-based calculation. That approach is consistent with the Defra metric guidance on degraded sites, which can require an earlier habitat to be used where land has previously been cleared, destroyed or degraded.

Importantly, the appellant’s Planning Statement had already set out two scenarios: one using gravel and another using a grass-covered baseline. The Inspector said this showed that the grassland scenario had been considered and that the appellant accepted grassland as the proper baseline.

Private gardens caused a genuine BNG problem

In the Harrow BNG appeal, the latest Small Sites Metric before the Inspector showed a net increase of 0.0421 habitat units, equivalent to a 30.04% increase. That sounds comfortably above the statutory 10% requirement, but the headline percentage was not the end of the story.

Much of the proposed gain depended on enhancing grassland and planting trees within the future gardens, alongside scrub around the edges of the site. The June 2026 Defra Statutory Biodiversity Metric User Guide says that post-development private gardens have no public access and biodiversity gains within them cannot be legally secured. Applying that guidance, the Inspector found that the long-term management and maintenance of the proposed garden gains could not be guaranteed.

The appellant tried to respond by reducing the garden depths so that the principal habitat areas would sit outside what was described as the private garden curtilage. The Inspector was not persuaded. In practical terms the land would still be within the residential property boundary and classified as private garden, so the proposed on-site arrangement did not itself secure the mandatory 10% gain.

That is an important point for applicants. A landscape plan cannot turn garden land into secure BNG habitat merely by drawing a different garden line. Our biodiversity net gain guide explains how the statutory metric, gain hierarchy and post-permission Biodiversity Gain Plan fit together.

The statutory condition changed the planning question

The BNG appeal then moved to a different question: did the failure of that particular garden-based solution mean planning permission had to be refused?

Current Planning Practice Guidance describes statutory BNG as a post-permission framework. For development subject to BNG, the Biodiversity Gain Plan is approved before development starts and is the mechanism for confirming how the minimum gain will actually be delivered. The guidance says it would generally be inappropriate to refuse an application simply because the biodiversity gain objective has not yet been demonstrated. Decision makers may, however, need to consider more broadly whether the statutory condition is capable of being successfully discharged.

In the Harrow BNG appeal, Inspector Teasdale found sufficient certainty. She noted that a section 106 agreement or another legal mechanism might, where appropriate, secure long-term on-site provision. More importantly, if garden-based gains were not viable, the statutory framework allowed other routes including registered off-site habitat gains or statutory biodiversity credits.

The decision records that both main parties regarded alternative delivery as realistic and achievable. On that evidence, the Inspector concluded that the biodiversity gain condition was “capable of being successfully discharged”. This was a case-specific finding, not a licence to submit an undeliverable BNG strategy and promise to sort it out later.

Planning Geek’s guide to section 106 agreements covers the wider use of planning obligations where long-term management or other enforceable commitments need to be secured.

No duplicate Biodiversity Gain Plan condition was needed

In the BNG appeal, Harrow had suggested a planning condition dealing with the Biodiversity Gain Plan. The Inspector omitted it.

Her reason was straightforward: the statutory biodiversity gain condition already applied, so a separate condition requiring the BGP would duplicate the statutory framework and Defra guidance. Current PPG makes the same distinction, strongly encouraging councils not to repeat the biodiversity gain condition in the list of ordinary conditions because it has its own statutory basis under Schedule 7A of the Town and Country Planning Act 1990.

That does not prevent an authority using additional, properly justified planning conditions for particular BNG matters where the tests for conditions are met. What was unnecessary here was simply restating the statutory BGP requirement. Our guide to discharging planning conditions explains the separate process for ordinary planning conditions.

The privacy refusal also attracted criticism

The BNG appeal was not only about ecology. Harrow’s first refusal reason concerned privacy and overlooking from proposed dormer windows, and that issue also fed into the full costs award.

The appellant had made clear that the relevant windows would be obscure glazed and fixed shut. Harrow accepted that this could deal with actual overlooking but continued to rely on actual and perceived overlooking as a reason for refusal.

Inspector Teasdale found that the Council had not adequately explained why perceived overlooking would remain unacceptable once the windows were obscure glazed and fixed shut. In the separate costs decision she said this amounted to “unreasonable behaviour” for the purposes of the Planning Practice Guidance.

The appeal permission therefore includes a condition requiring the relevant dormer windows to be obscure glazed and incapable of being opened.

Why Harrow was hit with full appeal costs

The Harrow BNG appeal also turned the Council’s handling of the biodiversity evidence into a costs issue. Harrow had focused on the incorrect gravel baseline calculation, yet the submitted Planning Statement expressly referred to a second scenario using grassland. The Inspector found that the Council had not properly engaged with that second scenario or asked for the specific metric if it considered the document missing.

In the BNG appeal, there was some uncertainty over precisely which metric documents had been before the Council at application stage. The Inspector did not simply assume the appellant’s account was correct. Even so, she found the grass-covered scenario was plainly identified within the Planning Statement and should have prompted further engagement.

Her criticism was pointed: “Co-operation and a more helpful approach” could have avoided the appeal altogether or narrowed the issues and reduced the expense.

Bringing the privacy and BNG issues together, the Inspector found Harrow’s unreasonable behaviour had caused unnecessary or wasted expense and justified a full costs award. The Council must pay Marlpark 71 HA4 Ltd’s costs of the appeal proceedings, with the amount to be agreed or assessed if agreement cannot be reached.

What the Harrow BNG appeal actually tells us

There are two lessons from this BNG appeal, and they pull in different directions.

First, councils and applicants still need to get the baseline and metric treatment right. Harrow succeeded on both of the underlying technical points which mattered most: historic grassland was the correct baseline and the claimed private-garden enhancements could not simply be counted as secure biodiversity gain. A high percentage in a metric is not enough if the habitat delivery behind it is not legally credible.

Second, a defect in the proposed BNG delivery route is not automatically the same thing as a planning reason for refusal. The statutory system deliberately leaves final delivery to the Biodiversity Gain Plan stage, provided there is sufficient evidence at application stage to conclude that the biodiversity gain condition can realistically be discharged.

That distinction also separates this decision from the recent Maidstone self-build BNG appeal, where the Inspector found the necessary application-stage information and legal mechanism were not in place and could not be treated as a detail for later.

The full Harrow BNG appeal decision is hosted by Planning Geek here, with the separate full costs decision here. The current GOV.UK biodiversity net gain Planning Practice Guidance and Defra statutory metric guidance provide the national framework applied in the appeal.