Planning changes usually create a line between what comes before and what comes after. Occasionally, that line produces a more interesting problem: two identical developments can face materially different obligations simply because their applications were submitted on different dates.

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The new biodiversity net gain exemption for development sites of 0.2 hectares or less is one of those occasions.

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From 6 August 2026, qualifying development on sites no larger than 0.2 hectares can fall outside mandatory biodiversity net gain, provided it does not impact onsite priority habitat. But the exemption does not reach backwards. An application submitted before 6 August remains subject to the previous regime even if it is still sitting undetermined when the new rules come into force.

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That creates an awkward cohort of live applications. A small development submitted on 5 August might carry a 10% BNG requirement through to delivery. The same scheme submitted on 6 August might not.

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The immediate reaction is that this is simply the consequence of transitional legislation. In legal terms, it is. In development terms, however, it creates a decision.

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If an application has not yet been determined, should the applicant continue with it, accept the BNG obligation and preserve its place in the planning process? Or could there be circumstances in which it is commercially better to withdraw the application and submit it again under the new regime?

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That is not as artificial a question as it initially sounds.

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Mandatory BNG can be relatively straightforward on some developments. On others, particularly small and constrained urban sites, it can influence layout, require offsite units, introduce additional professional costs and create another matter that has to be resolved before development can begin. The burden does not necessarily scale neatly with the size of the project. That concern was one of the reasons reform of BNG for smaller development was considered in the first place.

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For an applicant already struggling to make BNG work on a 0.15-hectare site, therefore, the new exemption has an obvious value. The difficult question is whether that value is greater than the value already embedded in the existing planning application.

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Planning applications acquire momentum.

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An application may have been through validation, consultation and several rounds of negotiation. Officers may have accepted the principle of development. Design amendments may have resolved neighbour concerns. Highways, heritage or other consultees may no longer be objecting. There may be a reasonable expectation of a delegated decision within weeks.

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None of that is a planning permission, but nor is it commercially meaningless.

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Withdrawing still means giving up the procedural position already established by the application. A replacement application starts a new determination process and may require consultation to run again. The direct fee consequence will depend on the circumstances: the planning fee regulations retain exemptions for certain repeat applications following withdrawal or refusal, so a resubmission may in some cases qualify for a ‘free go’. The more significant commercial question may therefore be the programme and planning risk involved in voluntarily starting the application process again.

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This is why the tactic makes most sense at the margins of the planning process rather than as a general response to the exemption.

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Take an application lodged shortly before 6 August which has only recently been validated. Assume the site is genuinely below 0.2 hectares, no priority habitat is affected, and the development has a difficult BNG position requiring the purchase of offsite units. Relatively little planning programme may yet have been invested in that application. Starting again could mean exchanging a modest delay for the removal of a delivery obligation that might otherwise affect cost and implementation.

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Now move the same application six months forward. The planning case has been negotiated, amendments have been agreed and the officer is preparing a recommendation for approval. The BNG work is substantially complete. Withdrawal may technically open the route to the exemption, but the commercial calculation has changed. The saving now has to justify surrendering a planning position that has taken months to establish.

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The interesting point is that the amount already spent on BNG is not really the right measure. That money is sunk. The relevant comparison is between the remaining burden of complying with BNG and the additional cost, delay and planning risk created by starting again.

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That distinction matters because developers can understandably become focused on recovering expenditure already committed to an application. Planning strategy should generally look forward instead. If £10,000 has already been spent designing a BNG solution but implementing it will cost another £75,000, that is a very different proposition from a scheme where the remaining obligation is largely administrative. Equally, saving £20,000 on ecology is unlikely to be attractive if a resubmission puts a valuable planning permission several months further away.

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There is another reason not to treat withdrawal and resubmission as a procedural trick. The applicant does not only restart the clock. It also reopens the planning judgement.

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Policy may have moved. New evidence may have emerged. An issue identified during the first application may become more difficult to resolve the second time around. An emerging local plan may carry greater weight. There may have been a relevant appeal decision. Conversely, the planning position may have strengthened.

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The question is therefore not simply whether BNG can be avoided. It is whether the whole planning position is sufficiently robust that voluntarily giving up the existing application is worth doing.

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The temptation to focus on the red-line boundary also needs care. A threshold based on a site area of 0.2 hectares inevitably makes the location of that line commercially significant. Applicants should certainly check whether historic application boundaries include land unnecessarily. But the answer cannot be to manufacture an application site that does not properly represent the development simply to achieve an exemption. The planning application must still make sense on its own terms.

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That is particularly important because exemption from mandatory BNG is not exemption from ecology. Priority habitat remains relevant to whether the new exemption is available at all, while protected species, designated sites, local development plan policies and conventional ecological mitigation continue to operate outside the statutory BNG regime.

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The better way to understand the change is therefore as a new variable in development strategy.

For some live applications, it will change nothing. Where BNG is inexpensive, the application is advanced or the planning balance is finely drawn, preserving momentum is likely to be more valuable than pursuing the exemption.

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But there will be another category: small sites submitted shortly before the rules changed, still at an early stage, where BNG is creating a genuine cost or delivery problem and where there is little planning advantage in maintaining the original submission date. Those applications deserve a closer look.

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There is also an important limit to waiting for permission and attempting to correct the position afterwards. The transitional provisions prevent the new small-site exemption being used through section 73 where the relevant original application or permission predates the new regime. The opportunity, where one exists, therefore sits principally with applications that are still live rather than permissions that have already been secured.

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That makes the timing unusually important.

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The Government has decided that certain small developments no longer need to deliver mandatory BNG because the burden is not considered proportionate. Yet, inevitably, the transitional arrangements leave some developments on the other side of that judgement purely because of when their applications entered the system.

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Applicants are not obliged to accept that procedural history without considering its commercial consequences.

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Withdrawal and resubmission will certainly not be right for every qualifying scheme. In many cases it would be a false economy. But where the application is young, the planning proposition is robust and BNG represents a meaningful remaining cost or constraint, starting again may be more than a technical possibility.

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It may be the better planning strategy.

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