Which reports a retail unit above the impact threshold needs
Out-of-centre retail development above the plan-set or default 2,500 m2 threshold has to pass both the sequential and impact tests. Here is the evidence base that carries it, and the order to commission it in.
A retail unit outside a defined centre crosses into impact assessment territory at 2,500 m2 of gross floorspace, unless the local plan has set a lower figure, and a great many plans have. Below the line you argue the sequential test alone. Above it you run two tests together, and the retail impact assessment threshold reports become the largest and most contested part of the application. The site constraints matter, but they are rarely what decides the case.
What follows is the evidence base an out-of-centre retail proposal above the threshold normally has to carry in England, and the order in which it is sensible to commission it.
Where the floorspace figure comes from
The National Planning Policy Framework asks for an impact assessment where retail and leisure development is proposed outside a town centre, is not in accordance with an up-to-date development plan, and exceeds a floorspace threshold set in the local plan. Where the plan is silent, the default figure is 2,500 m2 gross. The August 2026 edition of the Framework reorganised its chapters around policy codes rather than paragraph numbers, so check the current code on gov.uk before you quote it in a planning statement.
Two points get missed. The threshold is gross floorspace, not net sales area, so ancillary storage, staff areas and the service yard building all count. And the plan-set figure can be far lower than the national default: some authorities apply thresholds in the hundreds of square metres for sites near a fragile district centre. Read the adopted plan before you assume 2,500 m2 applies.
A proposal that does accord with an up-to-date plan allocation escapes both tests. That is worth establishing early, because it changes the budget by a large margin.
The sequential test and the evidence it needs
The retail sequential test asks whether the proposed use could be accommodated on a site in a centre first, then on an edge-of-centre site, before an out-of-centre location is accepted. The applicant has to show that a search was carried out and that no suitable and available sequentially preferable site exists.
The search area has to be defined and justified. Officers will push back on a catchment drawn tightly around the application site, so define it by reference to the plan's own centre hierarchy and to the catchment your own retail evidence uses. Then record, site by site, why each sequentially preferable candidate fails on availability, suitability or viability. A table with site name, area, ownership position, planning status and the reason for rejection is more persuasive than three pages of narrative.
Flexibility is where sequential tests fall over at appeal. You are expected to show reasonable flexibility on format and scale, and a case built on a fixed 4,000 m2 single-storey box with 200 surface spaces invites the finding that no flexibility was shown at all. Say what you tested and what you rejected, and why.
What goes into the retail impact assessment
A Retail Impact Assessment has to address two things: the impact on existing, committed and planned public and private investment in a centre in the catchment, and the impact on town centre vitality and viability, including local consumer choice and trade in the centre and the wider retail catchment.
The method is normally a quantitative trade draw analysis. You establish available expenditure in the catchment, estimate the turnover of the proposal from a floorspace and sales density assumption, then distribute the trade diversion across the affected centres and express the diversion as a proportion of each centre's existing turnover. Every input is arguable, which is why the assumptions schedule matters more than the output table.
The Planning Practice Guidance chapter on town centres and retail sets out how the tests should be approached and what an impact assessment should cover. It does not set a percentage at which harm becomes unacceptable, and neither does the Framework. Anyone who tells you there is a magic figure is quoting a local plan or an inspector's conclusion on a different set of facts.
Failure on either limb of the impact test is a policy reason for refusal in its own right. That asymmetry is the reason to scope the assessment with the case officer and the authority's retail adviser before commissioning it.
Health check evidence for the affected centres
The impact test only works if the baseline is real. A health check of each centre likely to be affected gives you that baseline, and the indicators the Guidance points to are the familiar ones: the diversity of uses, the proportion of vacant units and how long they have been vacant, retailer representation and demand, rental levels, footfall, accessibility, the perception of safety and the state of the environment.
Survey the centres yourself rather than relying on a desk exercise. Unit-by-unit frontage surveys with dates and photographs stand up to cross-examination. Desk-based vacancy figures of unknown vintage do not.
Where a centre is already fragile, expect the authority to argue that a small absolute diversion of trade is a large relative harm. That argument is hard to answer without a health check that says clearly what the centre's current trajectory is.
Transport, servicing and parking evidence
Retail generates trips at a rate that few other uses match on a per-square-metre basis, so the highway evidence is usually the second-largest cost after the retail work. A Transport Assessment is the normal requirement at this scale. The thresholds PlanScope uses to flag one are 2,500 m2 of floorspace or 50 or more dwellings, which is a useful starting point, though the local validation checklist and the highway authority's own guidance take precedence.
The assessment needs trip generation, junction capacity work at the accesses and the nearest sensitive junctions, a servicing and delivery strategy with swept-path drawings for the largest vehicle, and a parking assessment against the adopted standards. Do not leave the service yard to the detailed design stage. Refusals on the inadequacy of servicing arrangements are common, and they are avoidable.
A travel plan is often secured by condition or obligation rather than submitted up front, but drafting it early helps because its measures can offset trip generation in the transport case.
Economic and employment evidence
An Economic Impact Assessment does a different job from the retail impact work. The retail assessment is about harm to centres. The economic assessment is about the benefit side of the balance: construction employment, net additional operational jobs after displacement, business rates, and any regeneration effect on the site itself.
Be honest about displacement. A scheme that draws trade from a nearby centre also draws staff and turnover from the businesses there, and an assessment that reports gross job numbers without a displacement adjustment tends to get discounted entirely by the decision-maker. Net additional jobs, clearly derived, carry more weight than a large gross figure.
Where the site is an allocated employment site, an Employment Land Assessment may also be needed to justify the loss of employment land to retail. That is a separate policy test and a separate document.
Conditions on goods, subdivision and mezzanines
Assume the permission will be conditioned tightly, and plan for it. Authorities routinely restrict the range of goods that may be sold, cap the net sales area, prevent subdivision into smaller units and prevent the insertion of a mezzanine. The reason is that Class E of the Use Classes Order allows movement between shops, offices, cafes, clinics and indoor sport without a further permission, so without conditions the retail case you argued can be replaced by a different use overnight.
Mezzanines are worth understanding separately. Section 55(2A) of the Town and Country Planning Act 1990 makes the provision of a mezzanine floor development where the building is used for retail and the mezzanine exceeds 200 m2, so a large internal deck is not a free increase in floorspace.
Negotiate the wording rather than accepting a draft condition late in the process. A goods restriction that lists permitted categories precisely is easier to live with than one that defines the use by reference to the applicant's business model. And if you later need to vary it, you are applying under section 73 with the impact tests reopened, so the wording you accept now has a long life.
Enter your postcode on PlanScope to see which of the 66 reports your site is likely to need, with the retail thresholds applied to your floorspace figures. Browse the full list on the report index if you would rather work from the categories.
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 rather than legal advice, so check the position with your local planning authority or a qualified professional before relying on it.
Frequently asked questions
Is the 2,500 m2 retail threshold gross or net floorspace?
It is gross external floorspace, so storage, staff accommodation, plant rooms and back-of-house areas all count towards it. Applicants who measure only the net sales area regularly find themselves above the threshold once the authority remeasures. Check the adopted local plan first, because a plan-set threshold replaces the national default figure and can be very much lower.
Does an allocated site still need a sequential test?
If the proposal accords with an up-to-date development plan, including a site allocation for the use proposed, the sequential and impact tests in national policy do not apply. The difficulty is the words up to date and in accordance with. An allocation for mixed use that does not contemplate the retail floorspace you are proposing will not carry you past the tests.
How many centres does the impact assessment have to cover?
Every centre likely to experience a material trade diversion from the proposal, which is a matter for the catchment analysis rather than administrative boundaries. That often means centres in a neighbouring authority. Agree the list of centres with the case officer at scoping, because adding a centre after submission usually means redoing the trade draw and the health checks.
Can a condition stop the unit being split into smaller shops later?
Yes. Conditions limiting subdivision, capping net sales area and restricting the range of goods are standard on out-of-centre retail permissions, and they are normally held to be reasonable because they control the impacts the permission was assessed against. Varying one later means an application under section 73, which reopens the retail tests on the amended proposal.
Do I need an Economic Impact Assessment as well as the retail work?
Not always. Above the impact threshold it is usually worth having. The retail assessment deals with harm to centres and the economic assessment supplies the benefits side of the planning balance. Report net additional jobs after displacement rather than gross figures, because a decision-maker will discount unadjusted gross employment numbers.
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.