Evidence base for a scheme relying on a fallback position

A fallback argument says: refuse this and something worse will happen lawfully instead. It only works if you can show the worse thing would actually be built. The fallback position planning evidence that persuades an inspector therefore has two halves, and most submissions produce only the first. Half one is that an alternative development is lawful. Half two is that there is a real prospect it will be implemented if permission is refused.

Both halves are evidential. Neither is satisfied by asserting that permitted development rights exist.

What the argument claims, in planning terms

A fallback is a material consideration, not a policy test. You are inviting the decision maker to compare two futures: the scheme before them, and the lawful alternative that would follow refusal. Where the proposal causes less harm than the alternative, that comparison weighs in favour of permission even if the proposal conflicts with policy.

The argument is at its strongest in three settings. A permitted development right the applicant could exercise tomorrow. An extant planning permission capable of implementation. An established lawful use the applicant could resume or intensify.

It is at its weakest when the alternative requires a further consent, a third party's agreement, or an economic decision nobody has committed to.

Showing a real prospect of implementation

The courts have settled on a low but genuine threshold: there must be a real prospect, not merely a theoretical possibility, that the fallback would be carried out. A fanciful alternative carries no weight. Beyond that, the weight given is a matter for the decision maker and scales with how likely implementation looks.

The evidence that moves the needle is the evidence of commitment and capability.

• A lawful development certificate under section 191 or 192 of the Town and Country Planning Act 1990 confirming the alternative is lawful. This is the single most persuasive document available, because it removes the argument about lawfulness entirely.
• A prior approval already granted for the alternative, where the class requires one.
• An extant permission with its expiry date, evidence of a material start where one has been made, and the discharge position on conditions that must be satisfied before works begin.
• Drawings of the fallback at the same level of detail as the application scheme, not a sketch.
• A costed build programme or a contractor quotation showing the alternative is deliverable.
• A written statement from the applicant, and ideally from the landowner, that the alternative will be pursued on refusal.

Where the land is in someone else's control, deal with that head on. A fallback that depends on a third party doing something has to be supported by evidence about that third party, not about the applicant's intentions.

Evidencing the fallback scheme in detail

Treat the fallback as if you were applying for it. That is the discipline that separates arguments that land from arguments that are dismissed in a paragraph.

Draw it properly, at the same scale and in the same drawing set as the proposal. Quantify it: floorspace, height, number of units, parking, footprint, extent of hardstanding, trees affected. Then state its effects on the same receptors the proposal is assessed against, using the same methods.

The constraint evidence has to be done twice as well. If the site sits in a Source Protection Zone, both futures need the groundwater position addressed, because an inspector comparing two schemes wants the comparison to be like for like. The same applies where a known bat roost is present: an alternative that would destroy the roost cannot be presented as a lawful fallback without dealing with the separate licensing regime, since survey and mitigation licensing legally require a suitably licensed ecologist under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017.

Comparing harm properly

Set the comparison out as a table and keep the receptors constant.

Two drafting rules make the table credible. Concede where the proposal is worse on a receptor, because a comparison that favours the applicant on every line reads as advocacy. And avoid comparing against a deliberately bad fallback: a straw alternative nobody would build is the quickest way to lose the argument.

The comparison also has to deal squarely with permanence. A fallback that would be built and then remain for 60 years is a different comparison from one that could be reversed.

Where the argument usually fails

Four failures account for most of it.

The alternative turns out not to be lawful. Permitted development rights were removed by condition on an earlier permission, or by an Article 4 direction, or the limits of the class are exceeded once someone measures. This is why the certificate route is worth the fee and the eight-week wait.

The prospect is theoretical. Nobody has costed the alternative, nobody has said they will build it, and the applicant's own evidence shows the site is being promoted for the application scheme only.

The fallback is not a true alternative. It would not deliver the applicant's objective, so refusing the proposal would not lead to it. Inspectors notice when the fallback is a worse version of a different project.

The comparison is incomplete. The fallback is assessed on two receptors and ignored on the rest, so the decision maker cannot be satisfied the proposal is the lesser harm.

An illustrative example. An owner applies for a two-storey side extension that breaches the council's design guidance on the gap to the boundary. The fallback is a single-storey rear extension plus a large outbuilding, both within Part 1 of the General Permitted Development Order 2015. The case is made by obtaining a certificate of lawfulness for the proposed outbuilding first, drawing both options, and showing that the outbuilding would remove more of the rear garden and have a greater effect on the neighbour's outlook than the extension sought. The certificate converts an argument into a fact.

The submission pack

1. Planning statement with a dedicated fallback section setting out lawfulness, prospect of implementation and the comparison.
2. Drawings of the fallback to application standard.
3. A certificate of lawfulness, prior approval, or extant permission documents.
4. Technical notes assessing the fallback on the same receptors as the proposal.
5. A signed statement of intent from the applicant and, where relevant, the landowner.
6. Costings or a programme where deliverability is in question.

Check the local validation list before submission, because the fallback material is supporting evidence rather than a listed requirement, and officers sometimes miss it in an appendix. You can browse the report types to see which technical assessments your particular comparison will need on both sides.

And file the comparison table on the first page of the statement, not the last. An inspector who finds it early reads the rest differently.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. A Lawful Development Certificate is the only formal way to confirm that works or a use are lawful. PlanScope produces AI-assisted draft reports for planning applications, and reports should be reviewed before submission. PlanScope does not guarantee planning approval.