Who prepares a retail impact assessment

The retail impact assessment author needs market analysis skills that most planning consultants do not have. The assessment is an exercise in estimating where existing spending goes now, where it would go if the proposal were built, and what that shift means for the health of a defined town centre. That is retail economics with a planning wrapper, and a general practice planner writing it without survey data and a trade draw model produces something the council's own retail adviser will take apart.

For a small business considering a unit outside a centre, the first question is whether the assessment is needed at all.

What the assessment has to test

National policy requires an impact assessment for retail, leisure and office development outside town centres and not in accordance with an up to date development plan, where the floorspace exceeds a locally set threshold or, where the plan sets none, 2,500 m².

Two tests, and they are different:

• The effect on existing, committed and planned public and private investment in a centre or centres in the catchment.
• The effect on town centre vitality and viability, including local consumer choice and trade in the centre and the wider retail catchment, up to five years from the expected opening, or ten years for a major scheme forming part of a phased development.

A sequential test comes first and separately. It asks whether the development could be located in a centre, or on an edge of centre site, before impact is considered at all. A Sequential Test for retail that fails is fatal regardless of how favourable the impact conclusion is, so run it first.

Note what the impact test does not ask. It does not ask whether an existing trader will lose business to a competitor. Competition between retailers is not a planning consideration, and an objection framed that way fails.

Retail planning experience against general planning practice

The competence question splits into three parts, and different people often hold them.

The planning judgement. Applying the policy tests, framing the conclusion, and defending it at committee or inquiry. A chartered planner with retail casework experience does this.

The market analysis. Estimating available expenditure in the catchment, existing market shares, and the trade the proposal would draw from each centre and each existing store. This is a retail or economic analyst's work, and it relies on data sources and a modelling method the analyst can explain.

The centre assessment. Gathering health check evidence on the ground for each centre in the study area.

Where a single consultancy offers all three, ask which individual does the modelling and what they have defended at inquiry. Where the applicant's team lacks the middle piece, the assessment will read as narrative assertion, which is the most common reason these documents fail. Our note on checking whether a survey is still valid covers the related question of data currency, which bites hard here because expenditure patterns move.

Household survey data and where it comes from

Trade draw modelling starts from a household survey of shopping patterns in the catchment: where people do their main food shop, their top-up shop, their comparison shopping, and how they travel.

The options, with their consequences:

Two things a reviewer checks first. The sample size by zone, because a catchment split into eight zones with a small sample per zone produces market shares with wide error margins. And the survey date, because a survey predating a major store opening or closure in the catchment no longer describes the market.

Where the council's study is dated and no bespoke survey is affordable, say so plainly and run a sensitivity test showing how the conclusion changes on different market share assumptions. That is more persuasive than presenting stale figures as current.

Trade draw modelling competence

The model itself is a step by step calculation rather than a black box, and the person running it should be able to walk an officer through it.

1. Define the catchment and its zones, with a map and a reason for each boundary.
2. Establish population and expenditure per head by zone, with growth assumptions stated.
3. Establish existing market shares by store and centre from the survey.
4. Estimate the proposal's turnover, with the floorspace, sales density assumption and its source.
5. Allocate that turnover across zones and existing destinations, showing the diversion from each centre.
6. Express the diversion from each affected centre as a proportion of that centre's turnover.
7. Interpret the result against the health check evidence for each centre.

Step four is where assessments diverge most. A sales density taken from the operator's own trading patterns is defensible if evidenced. One taken from a general benchmark needs a stated source and a sensitivity range, because turnover drives everything downstream.

Step seven is the one that gets skipped. A given percentage of trade diversion means something quite different for a centre with high vacancy and a weak anchor than for a healthy market town, and the assessment has to make that connection rather than leaving a number hanging.

Health check evidence and who gathers it

Health checks are field work. Somebody walks each centre and records the evidence, and the indicators are conventional: the proportion of vacant units and their location within the centre, the mix of convenience, comparison, service and food and drink uses, the presence and condition of anchors, rents and yields where available, footfall where it can be counted or obtained, environmental quality, accessibility and parking, and any recent or committed investment.

Two points on method. Record the date and the day of the week, because a Tuesday in February and a Saturday in December are different centres. And photograph the vacant units, so the finding can be verified rather than argued about.

Councils increasingly have their own health check baselines in the local plan evidence base. Using the same indicators makes comparison possible and removes an easy line of attack. An Economic Impact Assessment may also be required where employment effects are in issue, and the two documents should use one consistent description of the proposal.

Review by the authority's own retail adviser

Assume the assessment will be reviewed by a specialist retained by the council, and write it for that reader.

What they will do: rebuild the model from your inputs, test the turnover assumption, check the survey's age and sample, look for diversion that has been spread thinly across many centres to keep each figure low, and check whether the health check evidence supports the interpretation.

What makes their job easy, and your position stronger: a clear inputs table, the survey data as an appendix, the model shown as a series of tables rather than described, and every assumption labelled with its source. Where you have taken a view the adviser might disagree with, say so and give the sensitivity.

Scoping it with the officer first

Do this before any survey money is spent. A scoping note of two or three pages, sent to the case officer and to the authority's retail adviser if one is already appointed, should set out:

• The proposed floorspace by type and the assumed operator or operator profile.
• The proposed catchment and zones, with a map.
• The centres to be assessed, and those proposed to be excluded with reasons.
• The survey data to be relied on, its date and its source.
• The sales density assumption and its basis.
• The assessment period, five or ten years, with the reason.

Agreement on those six points removes most of the argument later. Disagreement discovered at submission costs a round of consultation and often a fresh survey. A reviewer from the professional directory can also check a draft Retail Impact Assessment before it goes in. PlanScope drafts these documents structured to UK planning policy and flags missing data rather than inventing it. Reports should be reviewed before submission, and we do not guarantee planning approval. Councils usually expect a suitably qualified author for retail impact work, and professional review is strongly advised.

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