Planning permissions are often treated as fixed moments: the point at which uncertainty ends, value crystallises and development can begin. In reality, permission records a scheme at one stage in its life. Design continues, costs move, operators change and regulatory requirements develop. The consent may remain valid, but the project around it does not stand still.

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That creates a second planning exercise after permission has been granted. The task is no longer to establish whether development should happen in principle. It is to keep the approved scheme coherent, lawful and capable of being delivered as circumstances change.

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Some changes are physical. Detailed design may reveal that the building needs a different internal arrangement, altered servicing, additional plant or revised materials. An operator may want more bedrooms or different communal space. Individually, these adjustments can appear modest. Collectively, they may affect the description, approved drawings, conditions or assumptions behind the permission.

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Other changes are commercial. Construction costs rise, funding terms shift and markets weaken. Affordable homes secured through a Section 106 agreement may no longer attract a registered-provider purchaser on the anticipated terms. A development that was viable when approved can become difficult to implement even though its planning merits have not fundamentally changed.

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The planning system provides mechanisms for responding, but they do different jobs. Section 96A can make a non-material amendment. Section 73 can vary or remove conditions and creates a new permission alongside the original. A planning obligation may be changed by agreement through a deed of variation or, where the statutory requirements are met, through Section 106A.

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These routes are related, but they are not interchangeable. Changing an approved plan may require a Section 73 application. Changing an affordable-housing tenure, contribution or review mechanism may require the Section 106 agreement to be varied. Where both are affected, the processes may need to proceed together so that the permission and legal agreement describe the same deliverable scheme.

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That distinction matters because a permission is more than a set of drawings. Its operative description, conditions, approved documents and obligations form a connected legal structure. Amending one part without understanding the others can create a consent that is internally inconsistent or cannot safely be implemented.

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Section 73 is often more flexible than its description as a procedure for varying conditions suggests. Where approved plans are controlled by condition, it can accommodate material changes provided the resulting conditions do not conflict with the operative terms of the original permission. It cannot, however, change the description of development itself.

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Section 73B is intended to address part of that problem. Once brought into force, it should allow changes to descriptions as well as conditions where the resulting permission would not be substantially different from the existing consent. It promises a more realistic response to the way projects evolve, although “substantially different” will inevitably require judgement. As at August 2026, it has been enacted but is not yet available.

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Even then, amendment strategy will not become straightforward. Environmental assessment, habitats requirements, biodiversity obligations or the cumulative effect of earlier changes may limit what can safely be approved. Where several permissions exist, implementing one may also make another incapable of lawful completion.

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Planning obligations create a different form of rigidity. They secure affordable housing, infrastructure, contributions and management arrangements that may continue long after permission is issued. Those commitments make development acceptable, but drafting based on assumptions that later prove wrong can obstruct the delivery the agreement was intended to support.

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The difficulty in finding registered providers willing to acquire some Section 106 affordable homes is an obvious example. A scheme may reach construction or completion without a purchaser able to take the units. The original planning judgement was not necessarily mistaken. The delivery market may simply have changed.

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Government guidance has encouraged authorities to use existing powers pragmatically for qualifying uncontracted homes, including deeds of variation and Section 106A. This does not create a general right to reduce affordable housing. It recognises a narrower point: an obligation that cannot operate in the market may need to evolve if homes are to be occupied and the wider development completed.

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The strongest response is rarely to wait until delivery has stalled. Section 106 agreements can anticipate change through carefully defined cascades, substitution provisions, review mechanisms and alternative forms of provision. These should protect the planning outcome while allowing a workable response where the preferred purchaser, tenure or delivery route is genuinely unavailable.

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Flexibility must nevertheless be disciplined. A cascade that is too easy to trigger can dilute the public benefit used to justify permission. One that demands evidence which can never realistically be produced offers no useful flexibility. Good drafting defines the sequence, evidence, timescales and fallback position clearly.

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Viability presents a similar tension. The August 2026 National Planning Policy Framework assumes that policy-compliant proposals are viable, while recognising limited circumstances in which materially different development, unusual site characteristics, unforeseen costs or significant economic change may justify viability evidence.

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A viability appraisal remains a snapshot based on assumptions about costs, values, programme and obligations. It cannot guarantee that those assumptions will remain true through design, procurement and construction. Equally, a later deterioration in viability does not by itself establish that an obligation should be removed.

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Post-permission negotiations therefore require more than an updated spreadsheet. The applicant must explain what changed, what alternatives were tested and how the revised package would preserve the benefits and integrity of the original decision. The question is not simply whether the project is less profitable, but whether a proportionate change is needed to keep an acceptable development deliverable.

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This is why consent management should begin before permission is issued. Conditions need to be checked for sequencing and compatibility. Heads of terms should identify obligations dependent on third parties or future markets. The implementation strategy should consider which works will lawfully commence development and whether later amendments could affect completion.

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The same discipline should continue after determination. The permission, drawings, conditions, Section 106 agreement, Community Infrastructure Levy position and other approvals should be treated as a single consent architecture. Each proposed change should be tested against it before new drawings are finalised or works begin.

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A permission can lose value without expiring. A consent that no longer matches the intended building, contains obligations that cannot be performed or has been fragmented by poorly coordinated amendments may be technically extant but practically unusable. Conversely, a well-managed consent can absorb necessary change without reopening the principle of development.

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Planning permission therefore remains a major milestone, but it is not a guarantee of delivery. Its value depends on what happens next: discharging conditions, satisfying obligations, controlling amendments, preserving lawful implementation and responding intelligently when circumstances change.

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Permission, in other words, is no longer the end of the story. For many schemes, it is the beginning of a second planning exercise: keeping the consent alive, coherent and capable of being built.