Evidence base for a permission in principle application
The application is a form, a site plan and a fee. What permission in principle actually settles, and where the evidence base really lands.
Permission in principle settles three things and nothing else: the location, the land use and the amount of development. Everything that would normally fill an application pack is held back to the technical details consent stage. So the permission in principle documents you submit are deliberately thin, and the common mistake is sending too much rather than too little.
The route came in under the Housing and Planning Act 2016 and is set out in regulations. It works in two stages, and both have to succeed before you can build.
What permission in principle covers
Stage one grants permission in principle for housing-led development on a site, confirming that the principle of residential development of a stated scale in that location is acceptable.
Stage two is an application for technical details consent, which deals with layout, scale within the approved parameters, appearance, access, landscaping, drainage, ecology, contamination and everything else. Grant of technical details consent, taken with the permission in principle, is the planning permission.
Two routes lead to a permission in principle. An authority can enter a site on part 2 of its brownfield land register, which grants permission in principle automatically. Or a landowner can apply for it, which is the route most self-builders use.
The two-stage split has a real advantage. It establishes the principle before you spend money on surveys, which matters on a site where the answer to "will they accept a house here" is far from clear.
What is settled in principle and what is not
The in principle matters are location, land use and amount of development. The amount is expressed as a number of dwellings, usually as a range, and non-residential floorspace where there is any.
Everything else is a technical detail. That includes access arrangements, parking, drainage, trees, protected species, contamination, levels, materials and the relationship with neighbours.
This cuts both ways. An authority cannot refuse permission in principle because the access is awkward, but it can refuse technical details consent for exactly that reason, and permission in principle gives you no protection against it. A site with an unresolvable access problem will fail at stage two having passed at stage one, which is why a quick highways appraisal before you apply is worth the fee even though the authority will not ask for one.
Note also that permission in principle cannot be granted where the development is subject to environmental impact assessment, or where it would require appropriate assessment under the Habitats Regulations. In a nutrient neutrality catchment, that second limb takes the route off the table for many sites.
Site and use limitations
The route is restricted in scope.
- The development must be for housing-led development, meaning residential with any commercial element clearly secondary.
- The application route is limited to minor development, which means fewer than ten dwellings on a site of less than half a hectare.
- Development subject to environmental impact assessment is excluded.
- Development requiring habitats regulations appropriate assessment is excluded.
For a self-builder with a single plot or a small infill, those limits are rarely a problem. For anything above the small site threshold the comparison is with outline permission, which has no scale ceiling but requires a fuller application.
What the application has to contain
This is the part that surprises people. The application is short.
- A completed application form stating the proposed use and the amount of development, with the number of dwellings expressed as a minimum and maximum.
- A plan identifying the land, drawn to an identified scale with a north point, with the site outlined.
- The fee, which is charged per 0.1 hectare of site area under the fee regulations and is indexed annually, so check the current schedule.
There is no requirement for drawings of the proposed buildings, no design and access statement, no planning statement and no technical reports. An authority cannot refuse to validate the application for want of documents the regulations do not require.
A short covering note is often worth including anyway: the planning history, the reason the site is suitable, and any relevant allocation or settlement boundary position. Keep it to two pages. If the site is contentious, a one-page note addressing the obvious objection does more good than a full planning statement, which simply invites the authority to engage with detail it is not supposed to consider.
| Stage | What the authority decides | What you submit |
|---|---|---|
| Permission in principle | Location, land use, amount of development | Form, site plan, fee |
| Technical details consent | All other matters, within the approved parameters | Full drawings and the technical evidence base |
Publicity and the determination period
The authority must publicise the application in the prescribed way, and the publicity period is shorter than for a planning application. The determination period for a permission in principle application is five weeks, with the ability to agree an extension.
Five weeks is quick, and it means objections arrive compressed into a short window. Where neighbours are likely to object, it helps to have spoken to them first, because there is little time left to respond to a late objection before the decision is issued.
A permission in principle lasts for three years from the date it takes effect, within which the application for technical details consent has to be made. That is the date to diarise, because the whole benefit of the route is lost if it expires.
There is a right of appeal against refusal.
When the technical details stage arrives
Technical details consent is where the real work and the real cost sit. The determination period is five weeks for minor development, or ten weeks for major development, and the application must be consistent with the permission in principle.
What goes in depends on the site, and the authority's local validation list governs it as usual. On a typical single-plot or small infill site, expect to need site and block plans, floor plans and elevations, a drainage strategy, an ecology appraisal with a biodiversity net gain position, a tree survey where trees are present, and contamination information where the history suggests it.
Site-specific constraints drive the rest. On a site over sensitive groundwater the requirements described in the note on documents for a scheme in a Source Protection Zone apply, and a building with a known roost brings the position set out in the note on documents for a dwelling containing a known bat roost into play. A site crossed by an easement raises the issues covered in the note on documents for a site crossed by a public sewer.
Biodiversity net gain applies to the permission, and on a two-stage route the practical point is that the habitat baseline should be surveyed in the right season well before the technical details application. The statutory metric has to be completed by a competent person, and an AI-assisted draft is a starting point for that professional rather than a substitute.
Order the survey work in the gap between the two stages rather than after the second application is submitted. A bat emergence survey season missed at that point costs a year.
One honest comparison: for most small sites, outline permission and permission in principle end up costing something similar overall, and the choice turns on whether you need an early, low-cost answer on principle or a single application you can take to appeal with the detail attached. Where the principle is clearly acceptable, a full application is usually faster.
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. Browse the 66 report types to scope the technical details stage before you apply.
Frequently asked questions
What does permission in principle decide?
Location, land use and the amount of development, with the number of dwellings usually expressed as a minimum and maximum. Everything else, including access, drainage, ecology, contamination, levels and appearance, is a technical detail reserved to the second stage and cannot be used as a reason to refuse the first.
What documents are needed?
A completed form stating the use and amount of development, a plan identifying the land at an identified scale with a north point, and the fee, which is charged per 0.1 hectare and indexed annually. No drawings, design and access statement or technical reports are required, and an authority cannot demand them at validation.
Is there a size limit?
Yes on the application route, which is limited to minor housing-led development: fewer than ten dwellings on a site of less than half a hectare. Larger sites have to use outline permission or a full application instead, because the permission in principle application route does not extend to major development.
When can the route not be used?
Where the development is subject to environmental impact assessment, or where it would require appropriate assessment under the Habitats Regulations. The second exclusion matters in nutrient neutrality catchments, because it takes the route off the table for many otherwise suitable small sites in those areas.
How long does it take and how long does it last?
The determination period for a permission in principle application is five weeks, with extensions by agreement, and there is a right of appeal against refusal. The permission lasts three years from the date it takes effect, within which the application for technical details consent has to be made.
How is it different from outline permission?
Outline permission has no scale ceiling and reserves matters by condition, but it requires a fuller application with supporting documents. Permission in principle costs less and moves faster at the first stage and settles only three things. For small sites the overall cost is often similar, so the choice turns on how uncertain the principle is.
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.