Archaeology conditions: watching brief or evaluation

Deciding between a watching brief and a pre-determination evaluation is a risk decision, not an archaeological one. Trial trenching before determination costs money early and tells you what is there. A watching brief costs less and defers the discovery to the point where your groundworks contractor is on site and the programme has no slack. On a site with real archaeological potential, the second option is the expensive one.

County archaeologists advising local planning authorities apply a staged approach, and the stage the council asks for depends on how much is already known. Understand the stages and you can argue for the right one rather than accepting whatever the consultation response proposes.

The staged approach

Archaeological work in planning runs through five stages, and a site can enter or exit at any of them.

1. Desk-based assessment. A study of the Historic Environment Record, historic mapping, geotechnical data, aerial photography and lidar to establish known and potential remains.
2. Geophysical survey. Non-intrusive survey, usually magnetometry, to identify anomalies across an open site.
3. Trial trench evaluation. Intrusive sampling of a percentage of the site area to test what the earlier stages predicted.
4. Mitigation. Either preservation in situ through design changes, or preservation by record through excavation, strip, map and sample, or a watching brief.
5. Post-excavation analysis, archiving and publication.

National policy requires an applicant to describe the significance of any heritage assets affected, including any contribution made by their setting, and where a site may include assets with archaeological interest, to submit an appropriate desk-based assessment and, where necessary, a field evaluation. That wording, carried through successive editions of the National Planning Policy Framework and current in the edition published 17 August 2026, is the hook the county archaeologist uses when asking for trenching before determination.

What the desk study delivers

A desk-based assessment prepared to the standard and guidance of the Chartered Institute for Archaeologists sets out the known baseline and a statement of potential, usually expressed as low, moderate or high for each period.

Three outcomes are possible. A statement of low potential, accepted by the curator, can close the matter. A statement of moderate or high potential leads to further work. And an honest statement that potential cannot be established from the available sources, which is common on sites with deep alluvium or extensive later disturbance, leads to evaluation.

The desk study costs little relative to everything after it, and it should always come first. A site promoted through a local plan without one is a site whose archaeology risk sits entirely with the buyer.

When trenching comes before determination

Curators ask for pre-determination evaluation where the outcome could change whether permission should be granted at all, or could change the layout materially. That is usually the case where:

• The site sits within an Archaeological Priority Area or a similar locally designated zone.
• The desk study identifies high potential for remains of national importance, which could warrant preservation in situ.
• The scheme involves deep basements, extensive piling or a full-site dig that would destroy any remains present.
• Setting or scheduled monument issues mean that the answer affects the principle of development.

Where the answer only affects how mitigation is carried out, and not whether the scheme can proceed, a condition is the proportionate route. The distinction is set out more fully in our note on archaeological evaluation before or after determination.

Evaluation is normally specified as a percentage sample of the developable area, agreed with the curator in a written scheme of investigation before any machine goes on site. The design of the trench layout matters as much as the percentage, and our note on designing an archaeological field evaluation covers how to set it out.

Watching brief scope and its limits

A watching brief, more precisely an archaeological monitoring and recording exercise, places an archaeologist on site during groundworks with authority to stop or slow the work when something appears.

It suits sites where potential is low but not nil, where the groundworks footprint is small, or where earlier disturbance means survival is patchy. It is a poor fit where remains are likely to be extensive, because the archaeologist has no control over the sequence, the weather or the plant, and recording under those conditions is compromised.

Three limits to understand before agreeing to one:

• A watching brief records what the excavation happens to expose. It does not investigate.
• If something of importance appears, the work stops. There is no contractual mechanism that prevents that, and the delay lands on the critical path.
• The cost is open-ended. A brief priced for six weeks of attendance becomes an excavation if the trench cuts a cemetery.

Strip, map and sample

Between a watching brief and full excavation sits strip, map and sample: the topsoil is removed under archaeological supervision across a defined area, the exposed features are planned, and a sample of them is excavated and recorded.

It fits where evaluation has shown archaeology is present and reasonably well understood, where the whole footprint will be stripped anyway, and where the remains are of regional rather than national importance. The advantage over a watching brief is that the archaeologist controls the stripping sequence and the programme can be planned rather than gambled on.

The cost of deferring

Deferring investigation to a condition moves the discovery to the worst possible moment. Three consequences follow.

The first is contractual. Groundworks are under way, plant is on hire and the archaeologist's stop notice has no equivalent in the building contract's relief events unless someone drafted one. Check whether archaeology is a relevant event before signing.

The second is design. Remains found during construction can only be dealt with by preservation by record or by redesign, and redesign at that stage may need a section 73 application or a fresh permission. Remains found at evaluation stage can be designed around, which costs less and often makes better archaeology.

The third is funding. Lenders and buyers discount a site with an undischarged archaeology condition and an untested baseline. Discharging the condition in principle, with an agreed written scheme of investigation, removes part of that discount even before any digging happens.

Negotiating the condition wording

The standard three-part archaeology condition is worth insisting on, because a single-sentence condition leaves everything to be argued later. The three parts are:

1. No development to take place until a written scheme of investigation has been submitted to and approved in writing by the local planning authority.
2. The archaeological works to be carried out in accordance with the approved scheme.
3. The post-excavation analysis, archive deposition and publication to be completed in accordance with a timetable within the approved scheme, with the site not occupied until a stated stage is reached.

Three points to press on:

• Tie the trigger to the start of intrusive groundworks rather than to any development, so that site set-up and fencing are not caught.
• Ask for the third limb to be triggered by occupation of a phase rather than the whole site on a phased scheme.
• Resist wording that requires the whole post-excavation programme, which can run for years, to complete before any occupation.

Where the scheme also affects a standing building, the recording obligation runs in parallel, and a Historic Building Recording exercise may be conditioned alongside.

Programme and contingency

Build the archaeology into the programme as a named activity with a float allowance, not as a risk line in the appraisal. Evaluation needs the written scheme approved first, then fieldwork, then a report the curator has to read and respond to. On a moderate site that sequence takes longer than the eight weeks people assume.

And put the archaeological consultant in front of the curator early. A pre-application conversation about the scope of evaluation, agreed before the application is validated, is the single change that most reduces the eventual cost. Where a heritage asset is also in play above ground, the reasoning should sit in the Heritage Statement rather than in a separate note.

This is general guidance, not legal advice. Archaeological requirements are set by the curatorial adviser to your local planning authority, so check the position with them or with a qualified archaeologist before fixing a programme.

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