Fallback position in planning and the real prospect test

A fallback position is the argument that if the application before the authority is refused, something else lawful will happen on the site instead, and that the something else would be as harmful or more harmful than what is proposed. It works by changing the comparison. Instead of measuring the proposal against an empty site, the decision maker measures it against the alternative the applicant would actually build.

The test is not whether the fallback is probable. The Court of Appeal in Mansell v Tonbridge and Malling Borough Council treated the question as whether there is a real prospect of the alternative being implemented, which is a lower bar than likelihood, with the weight given to the fallback then varying according to how real that prospect is.

That two-stage structure, existence then weight, is where most fallback arguments come apart.

What a fallback argument asserts

Three things have to be true for the argument to run at all. The alternative has to be lawful, whether through an extant permission, a prior approval, permitted development rights or an existing lawful use. It has to be capable of being carried out. And there has to be a real prospect that the applicant or owner would carry it out if refused.

The comparison then has to favour the proposal. A fallback that is less harmful than the application is no help, and pointing at it merely hands the authority a better scheme to refer to.

Officers see weak versions of this constantly. A developer says that if the five-flat conversion is refused they will instead build a large rear extension under permitted development. If no drawings exist, no building regulations application has been made and the extension would be commercially pointless, the assertion carries almost nothing.

The realistic prospect test

What makes a prospect real is evidence of intention and of capability, together. Intention without capability is a wish. Capability without intention is a theoretical possibility.

Evidence that moves the needle:

• an extant permission with time remaining, and a lawful start made or capable of being made
• a prior approval granted for the alternative, with the conditions discharged
• a lawful development certificate confirming the alternative is permitted development
• costed drawings, a contractor appointment or a building regulations submission for the alternative
• a commercial case showing the fallback produces a return the owner would accept

The sequencing point is practical. Where a fallback rests on permitted development, obtaining a certificate of lawfulness for a proposed use or development under section 192 of the Town and Country Planning Act 1990 converts an argument into a fact. It costs a fee and some weeks, and it removes the authority's best line of attack.

And check the permission is still implementable. A consent with an undischarged pre-commencement condition and three weeks of its life left is not a fallback, and relying on it invites an inspector to say so in terms.

Comparing harm between fallback and proposal

The comparison has to be like for like and it has to be clear about which harms are being compared. A fallback may be worse in massing while being better in highways terms, and the decision maker weighs the planning balance as a whole rather than picking the single measure that suits the applicant.

Set it out as a table in the statement rather than in prose. Footprint, volume, height, window positions, parking provision, trees lost, and any designation-specific measure such as volume in the Green Belt. Where the fallback is worse on a particular measure, quantify by how much.

One common error is comparing the proposal with the most aggressive version of the fallback that could theoretically be built, rather than the version there is evidence the owner would build. Inspectors notice the difference, and an overstated fallback damages the credibility of the rest of the case.

Where the argument usually fails

Four failure modes recur.

The permission relied on has lapsed, or cannot be implemented because of a condition or because a ransom strip blocks access. The alternative is theoretical, with no drawings, no costings and no sign anyone intends to build it. The fallback is commercially irrational, so a reasonable owner in the applicant's position would not pursue it. Or the harm comparison does not actually favour the proposal once all the relevant measures are set out.

A fifth, subtler failure: the fallback would need a further consent that is itself uncertain. A fallback that depends on a future prior approval the authority might refuse is not a fallback. It is a hope, and hope attracts little weight.

An illustrative case using a prior approval

The following example is illustrative and not drawn from a real decision.

An owner of a vacant two-storey office building applies for planning permission to demolish and rebuild as six flats with a modest increase in height. The authority refuses on design grounds. The owner holds a prior approval under the commercial to residential provisions of the General Permitted Development Order, granted 14 months earlier, permitting conversion of the existing building to seven flats with no external change and a poorer internal layout.

The fallback here is strong. The prior approval exists, time remains, the conversion costs less than the rebuild and the owner has a tenant-free building earning nothing. On appeal, the comparison becomes the proposed scheme against seven flats of lower quality in the existing envelope, which changes the design argument substantially.

Weaken any one element and the argument thins. Let the prior approval lapse, or show the conversion needs works the class does not permit, and the authority is back to comparing the proposal with a vacant office.

How officers record the conclusion

A delegated or committee report that accepts a fallback will usually say three things: that the alternative is lawful and implementable, that there is a real prospect of implementation on the evidence supplied, and what weight the fallback is given in the balance. The weight language matters, because moderate weight and substantial weight produce different outcomes when harm is finely balanced.

If the officer's report omits the fallback altogether, that is worth raising before the decision rather than after. A decision taken without considering a material consideration that was properly put to the authority is vulnerable, and the straightforward remedy is usually to put the evidence in again in writing.

Where the fallback involves varying an existing consent rather than building something different, the mechanism is a different one, and the choice between routes is set out in the guidance on section 73 variation of planning conditions. A fallback argument also interacts with planning history on the same site, and the weight an earlier decision carries is covered in weight given to a previous refusal.

A Planning Statement drafted on PlanScope can set out the fallback as its own section, with the lawfulness, prospect and comparison headings separated so the evidence for each is visible, and the wider report library covers the supporting documents a contested application needs. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.