The two retail impact tests on vitality and investment
An out of centre retail proposal above the floorspace threshold faces two distinct impact tests. Merging them in one chapter is how applications lose the argument.
A retail or leisure proposal outside a town centre that is not in accordance with an up-to-date development plan faces two separate impact tests, and a planning statement that merges them loses the argument. The first asks whether the proposal would harm existing, committed and planned investment in a centre within the catchment. The second asks whether it would harm the vitality and viability of a centre, including consumer choice and trade. Both sit in the National Planning Policy Framework, both apply above a floorspace threshold that defaults to 2,500 m² gross unless the local plan sets a different figure, and an adverse impact of sufficient scale on either one is a reason for refusal.
They are not variations on the same question. Different evidence answers each.
The investment test and what it protects
The investment test looks forward. It protects schemes that have been committed or planned in a centre, which in practice means extant permissions, allocations in the development plan, council-led regeneration projects and private investment that has reached a stage where it can be evidenced.
The question is whether the proposal would undermine the deliverability of that investment. A food store proposal that would take enough trade to make a committed town centre scheme unviable fails this test even if the centre itself is currently healthy.
Three things make the assessment credible. Identify the investment specifically, with its reference number or plan allocation and its current stage. Say what the proposal would do to it, with reasoning rather than assertion. And address timing, because investment that is years from delivery and has no funding attached carries less weight than a scheme on site.
The test is also where an applicant can go on the offensive. Where the only committed investment in a centre is a long-standing allocation with no prospect of coming forward, say so with evidence, and the test loses much of its force.
The vitality and viability test
This test looks at the centre as it is. Vitality means how busy and active the centre is; viability means its capacity to attract continuing investment. The assessment has to address local consumer choice and trade in the centre and the wider catchment, scaled to the nature of the proposal.
The two sides of it are the quantitative trade impact and the qualitative condition of the centre. Neither works alone. A 12 per cent diversion from a strong centre with low vacancy and diverse uses may be absorbed. The same diversion from a centre with high vacancy, a narrow offer and one anchor store may not.
A retail impact assessment brings both together, and the structure that survives scrutiny sets out the centre health position first, then the quantitative work, then a reasoned conclusion that connects them.
Trade diversion and how it is modelled
The quantitative work follows a standard sequence, and each step is a place where assumptions can be challenged.
| Step | What it produces | Where it is challenged |
|---|---|---|
| Define the catchment and zones | The study area for the assessment | Zone boundaries drawn to suit the answer |
| Household survey or secondary data | Existing shopping patterns by zone | Survey age, sample size, question wording |
| Turnover of the proposal | Expected trade draw, from floorspace and sales density | Sales density source and whether it is company specific |
| Diversion assignment | Trade drawn from each existing centre and store | Assignment by judgement with no stated basis |
| Design year comparison | Impact as a proportion of centre turnover | Choice of design year and growth assumptions |
The design year matters more than most applicants expect. The assessment should test the first full year of trading after the proposal opens, and the Framework contemplates a longer horizon for major schemes, so expect to be asked for a later year as well. Commitments have to be in the baseline, which means the turnover of other permitted but unbuilt schemes is assumed to be trading.
Sales density is the single most argued input. Use a figure you can source and state the source, and run a sensitivity test. An assessment with one scenario invites the consultee to produce a second one that is less favourable.
Health check indicators for a centre
The qualitative side uses a set of indicators that has been in use since well before the current Framework, and the Planning Practice Guidance on town centres and retail remains the reference for them. The ones that do the work in practice:
- Vacancy, measured as a proportion of ground floor units and of floorspace, with a trend over at least three years
- Diversity of uses, including the balance of convenience, comparison, service and food and drink
- Retailer representation and any known requirements for space in the centre
- Rents and yields where evidence is obtainable
- Pedestrian flows, with the survey date and method stated
- Accessibility, car parking provision and public transport
- The physical condition of the public spaces and the shopfronts
Walk the centre and photograph it. A health check written from a desk, with vacancy counted off an online dataset, reads as exactly that, and officers in the authority know their own high street better than any consultant.
Cumulative impact with other commitments
Cumulative impact is tested, not just solus impact. That means assessing the proposal alongside other permitted schemes and allocations in the catchment, and presenting both figures.
Two traps appear regularly. The first is a baseline that includes commitments for the purpose of showing a small solus impact, but excludes them when calculating the cumulative figure. The second is an inconsistent treatment of a competing scheme, treated as trading in one calculation and absent from another. A consultee will find both.
Where the authority is assessing more than one application in the same period, expect it to run its own cumulative scenario. Offering that scenario first is usually better than having it produced against you.
The point at which impact becomes unacceptable
The Framework uses the words significant adverse, and attaches no percentage. That is deliberate, and attempts to establish a numerical rule of thumb have not survived contact with decision makers.
What the threshold responds to is the condition of the receiving centre. The same percentage diversion produces different conclusions depending on vacancy, the diversity of the offer, dependence on a single anchor and whether the centre is already in decline. So the conclusion has to be expressed as a judgement about the centre, supported by the numbers, rather than as a number with a conclusion appended.
Where the sequential test has not been passed, the impact tests do not rescue the proposal. The two run separately, and our sequential test for retail page sets out how the earlier question is approached.
Presenting the case for a town centre location
If a town centre or edge of centre site exists and is available, the honest answer is to use it. Most refusals start here. Where the evidence shows no suitable site exists, the submission is stronger for addressing the following in order:
- The sequential test, with the sites considered and the reasons each was discounted on suitability, availability and viability
- The investment test, naming the committed and planned investment and dealing with each
- The centre health check, with current survey work
- The quantitative impact, solus and cumulative, with sensitivity scenarios
- The planning balance, including economic benefits evidenced rather than asserted
An economic impact assessment is where employment and expenditure effects belong, kept separate from the impact tests so that benefits are not used to answer a harm question. Where viability arguments are deployed about the deliverability of a centre site, the analysis follows the same discipline as any other appraisal, covered in independent review of a viability appraisal.
Start the impact evidence before the design is fixed. The catchment survey takes time, and a scheme sized to a sales density that cannot be sourced is a scheme that will be re-run at the authority's request.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
When does the retail impact test apply?
To retail and leisure proposals outside a town centre that are not in accordance with an up-to-date development plan, above a floorspace threshold. The national default is 2,500 square metres gross, but a local plan can set a lower locally appropriate threshold, so check the adopted plan before assuming the national figure applies.
What is the difference between the two impact tests?
The investment test is forward looking and protects existing, committed and planned investment in centres within the catchment, asking whether the proposal would undermine its deliverability. The vitality and viability test looks at the centre as it is, covering trade, consumer choice and the health of the centre.
Is there a percentage of trade diversion that is automatically unacceptable?
No. The Framework asks whether the adverse impact is of sufficient scale, and sets no figure. The same diversion can be acceptable for a strong, diverse centre and unacceptable for one with high vacancy and a single anchor, so the conclusion has to be a judgement about the centre supported by the numbers.
Do I have to assess cumulative impact as well as solus impact?
Yes, and both figures should be presented. Permitted but unbuilt schemes and plan allocations in the catchment belong in the assessment, treated consistently across every calculation. Including commitments to show a small solus impact while omitting them from the cumulative figure is the error consultees look for first.
Can economic benefits outweigh a serious adverse retail impact?
That is a planning balance question for the decision maker, and the Framework treats a serious adverse impact on either test as a reason for refusal. Keep employment and expenditure benefits in a separate economic assessment so that benefits are not presented as an answer to a harm question.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.