The retail impact test and the 2,500 square metre hurdle

The retail impact test applies to main town centre uses proposed outside a town centre where the floorspace exceeds a threshold, and the default threshold in national policy is 2,500 m² gross unless the local plan sets a different figure. Below the threshold, no impact assessment is required. Above it, the application has to show that the proposal would not have an unacceptable effect on a defined centre, and failure on that test is a reason for refusal in its own right.

The sequential test is separate and comes first. Plenty of schemes pass the impact test and fail the sequential one, and the two answer different questions.

What the impact test asks

National policy sets two limbs, and both have to be addressed.

The first is the impact on existing, committed and planned public and private investment in a centre or centres in the catchment. That means schemes with planning permission, allocations in the local plan, and public space or infrastructure investment the council has committed to. A proposal that would undermine a town centre regeneration scheme already funded is the clearest case.

The second is the impact on town centre vitality and viability, including local consumer choice and trade in the town centre and the wider retail catchment. The assessment period runs to five years from the time the application is made, extended to ten years for major schemes phased over more than five years.

The wording of the test is worth holding on to. Refusal follows where the proposal is likely to have a significant adverse impact, not merely some impact. Every new retail development diverts some trade, and demonstrating that a centre would lose a share of turnover does not by itself defeat a scheme.

The threshold and where it changes

The 2,500 m² default applies only where the development plan does not set a locally appropriate threshold. Many plans do set one, based on the size and sensitivity of their centres, and those local figures are commonly a good deal lower.

Three points on measurement come up repeatedly. The threshold is expressed as gross floorspace, not net sales area. It covers main town centre uses generally rather than retail alone, so leisure, offices and food and drink can be caught. And extensions count, which means a series of small additions to an out-of-centre store can cross the figure cumulatively.

The test does not apply where the proposal accords with an up-to-date development plan, or where the site is within a defined centre. Check the policies map before commissioning anything, because centre boundaries are drawn tightly and a site on the far side of a car park may be out of centre even though it feels central.

Where the threshold is crossed, a Retail Impact Assessment is the document that answers it.

How impact is actually measured

The method is a trade draw and diversion exercise, and it is arithmetic rather than opinion.

1. Define the catchment and divide it into zones, usually from a household survey or from published population and expenditure data.
2. Establish the turnover of the proposal by applying a company average or benchmark sales density to the net sales area.
3. Distribute that turnover across the zones, showing where the trade would come from.
4. Convert the diversion into a percentage of the turnover of each affected centre, allowing for existing commitments already consented but not yet trading.
5. Set the result against a health check of each centre.

The health check is what turns numbers into a judgement. Vacancy rates and their trend, retailer representation, footfall, rents and yields, environmental quality, and the presence of anchor stores all indicate whether a centre can absorb a given level of diversion. A centre with low vacancy and a strong anchor absorbs a diversion that would damage one with a failing anchor and a rising vacancy trend.

Benchmark sales densities come from published company data and from comparable schemes, and they carry a lot of weight in the outcome. A figure taken from a different store format, or from a study several years old, changes every number downstream of it.

Cumulative impact is the part most often done badly. Consented but untraded floorspace has to be included, and so do other applications under consideration where the authority is aware of them. Leaving them out produces a figure the council's own retail adviser will simply redo.

Where the impact test follows the sequential approach

The sequential test asks whether there are sequentially preferable sites, meaning town centre first, then edge of centre, then out of centre. The impact test asks what the proposal would do to the centre if built. An application outside a centre needs to satisfy both.

Sequence matters in drafting. If the sequential assessment is weak, the impact case rarely rescues it, because national policy treats failure of the sequential test as a ground for refusal on its own. The Sequential Test (Retail) and the impact assessment should be written together by the same author, so their assumptions about format and scale match.

Flexibility is the link between them. A sequential assessment that considers only the exact format proposed will be criticised for lack of flexibility, and an impact assessment built on a smaller, more flexible format produces a different diversion figure. Keep them consistent.

Making the case, and where it usually goes wrong

Four things separate an assessment that convinces from one that does not.

Use a real catchment. A drive-time isochrone drawn without regard to competing centres, rivers or trunk roads produces diversion figures nobody believes.

Justify the sales density. A benchmark taken from a company average for a different format, or a figure from an old study, is the assumption most often challenged, and it drives every number after it.

Address the qualitative side. Impact on consumer choice, on the range of goods available locally, and on linked trips is part of the test, and a purely quantitative report leaves those points to the objector.

Say what the scheme adds. Investment, employment and expenditure retained in the area are proper considerations, and an Economic Impact Assessment gives the officer something to weigh in the balance rather than a list of harms with nothing beside it.

Retail impact reports are also read by a consultant acting for the council, and increasingly by objectors with their own adviser. Write the assumptions in a table near the front, with a source against each one, so the argument happens over the inputs rather than over what you meant.

One honest caveat. Retail impact work rests on survey data and on assumptions about how people shop, and both age quickly. If your household survey is more than a few years old, expect the council's adviser to say so, and budget for a refresh rather than defending stale figures.

For a view of the other documents an out-of-centre proposal is likely to need, browse the index of report types by category. 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.