Sources and consultation in an archaeological desk study

The quality of an archaeological desk-based assessment is decided by its sources. Two reports on the same site can reach opposite conclusions about archaeological potential because one consulted the Historic Environment Record, the county series mapping and the site's own boreholes, and the other consulted the National Heritage List and a web search. A developer paying for the report should know which sources were used, what each one can and cannot show, and which of them the county archaeologist will check.

An assessment prepared to the Chartered Institute for Archaeologists standard is an assessment of the known and potential archaeological resource within a defined area, using existing written, graphic, photographic and digital information. It is a synthesis of other people's records. So the list of records consulted is the evidence base, and an unsourced statement of potential is worth nothing.

What a desk-based assessment is scoped to do

The assessment has three jobs. Establish what is already recorded within and around the site. Assess the potential for remains that are not recorded, by period and with a stated confidence. And state the significance of what may be present, so the decision-maker can weigh harm against public benefit.

It cannot confirm the absence of archaeology. That distinction matters commercially, because a report concluding low potential does not remove the risk of a discovery on site, and the mitigation condition will usually still be imposed. What a good archaeological desk-based assessment does is narrow the risk enough to programme and price the next stage.

National policy sets the requirement. The Framework asks applicants to describe the significance of any heritage assets affected, including any contribution made by their setting, and where a site includes or has the potential to include heritage assets with archaeological interest, to submit an appropriate desk-based assessment and, where necessary, a field evaluation. The current edition was published on 17 August 2026 and uses policy codes rather than paragraph numbers, so cite the code from the published text at the time you write and check the wording rather than copying an older reference.

The Historic Environment Record search

The Historic Environment Record is the primary source, held by the county council, the unitary authority or, in London, by the Greater London Historic Environment Record. It holds monument records, find spots, historic landscape characterisation, event records for previous archaeological work, and often grey literature reports that appear nowhere else.

Order the search formally and keep the response. A named officer, a date, a defined study area and a returned dataset with record numbers is what makes the assessment checkable, and most services charge a fee and take a working week or two. Requesting it in week one of the programme is the least expensive piece of risk management on an archaeologically sensitive site. The mechanics are set out in more detail under searching a Historic Environment Record before you apply.

The search area needs a justification rather than a default. A small urban infill site with deep Roman stratigraphy may need only 250 m, while a rural site on a river terrace needs a kilometre or more to pick up the pattern of cropmark enclosures around it. The reasoning behind the choice is covered under the study area and search radius.

Three further record sets belong alongside the Historic Environment Record rather than instead of it. The National Heritage List for England for designated assets, which is the authoritative source for scheduled monuments, listed buildings, registered parks and gardens and registered battlefields. The Historic England Archive and its research records. And the Portable Antiquities Scheme database, which records finds reported by the public and often provides the only evidence of activity in a field that has never been surveyed.

Historic mapping and aerial photography

Historic mapping tells you about land use, truncation and the survival of earlier features. Work backwards through the sequence and record the date of survey rather than the date of publication, because they can be decades apart.

• Ordnance Survey county series at 1:2500 and 1:10560, first and second editions, which between them cover most of England from the mid nineteenth century.
• Tithe maps and apportionments from the late 1830s and 1840s, which name fields and give land use.
• Enclosure awards and estate maps, which are earlier again and often show ridge and furrow, moated sites and former settlement.
• County and town maps from the seventeenth and eighteenth centuries for broad layout and route ways.

Aerial photography adds what maps cannot. The RAF vertical survey of the 1940s covers almost the whole country before post-war development and before the worst of the plough damage, and it is often the best evidence of cropmarks and earthworks on a site that is now built over. Later Ordnance Survey and commercial coverage shows how the site changed. Lidar terrain models reveal low earthworks under woodland and pasture that are invisible on photographs.

Say which collections you searched, the dates of the sorties or flights, and what you saw. A report that states "aerial photographs were examined" without listing them is not reproducible, and an objector's archaeologist will say so.

Borehole and geotechnical data as archaeological evidence

Ground investigation data is the most under-used source in the whole assessment, and on deep urban sites and floodplain sites it is the most informative. Borehole logs and trial pit records show the thickness of made ground, the depth to natural deposits, the presence of alluvium, peat or colluvium, and any evidence of truncation.

That translates directly into archaeological conclusions. Two metres of nineteenth-century made ground over undisturbed brickearth means remains are likely to survive, deeply buried, and that the foundation design decides whether they are affected. A site cut back to bedrock in the 1960s has little potential regardless of what the Historic Environment Record says about the surrounding streets.

The sources are the British Geological Survey's borehole scans, the site's own ground investigation where one exists, and neighbouring site investigation reports held by the council. Where the site sits on a river floodplain, a geoarchaeological deposit model built from the borehole logs is the proper tool, because it identifies palaeochannels and buried land surfaces with potential for prehistoric material that no map or photograph will show.

Commission the ground investigation and the desk-based assessment in a way that lets the archaeologist see the logs. On too many projects the two reports are written in parallel by teams who never exchange data.

Building the potential statement period by period

The potential statement is the part the county archaeologist reads first. Structure it by period, from the palaeolithic through to the modern, and for each period give three things: what is recorded within the study area, what that implies for the site itself, and a rated potential with the confidence behind it.

Rate the potential in words you define. Nil, low, moderate and high are conventional, and the report should say what each one means for the likelihood and the character of remains. Then state significance separately, because a moderate potential for remains of high significance is a different planning problem from a high potential for remains of low significance.

Avoid the two standard failures. Listing every record within a kilometre without analysing it produces a gazetteer rather than an assessment. And concluding "the site has archaeological potential" without naming a period or a class of remains gives the adviser nothing to scope an evaluation against.

When field evaluation becomes necessary

Field evaluation follows where the desk sources cannot resolve the question and the answer would change the decision. In practice that means moderate or high potential for remains whose significance could be affected by the proposal, or any proposal near a scheduled monument or a nationally important site.

The choice is between pre-determination evaluation and a condition. Advisers normally ask for pre-determination work where the potential remains could be so significant that they might justify refusal or a redesign, because a condition cannot cure a scheme that should not have been permitted. For most sites a staged condition covering a written scheme of investigation, evaluation, mitigation, post-excavation analysis and publication is proportionate. An archaeological field evaluation has its own reporting structure, set out under the field evaluation report structure.

Programme the seasons. Trial trenching on arable land is easier between harvest and drilling, and a requirement for pre-determination evaluation discovered at week ten of a thirteen-week determination period costs months.

Consulting the archaeological adviser before you submit

The local planning authority takes advice from a county archaeologist, an in-house archaeologist, or in London from the Greater London Archaeological Advisory Service. Historic England advises on scheduled monuments and on remains of national importance.

Write to the adviser before the assessment is finalised, with the site boundary, the proposed development, the foundation and basement design, and the study area you propose. Ask three questions: whether the study area is acceptable, whether pre-determination evaluation is expected, and whether any known constraint has not reached the Historic Environment Record. Put the reply in the application.

Councils normally expect a desk-based assessment to be written by a suitably qualified archaeologist working to the Chartered Institute for Archaeologists standard, and professional review before submission is strongly advised. PlanScope drafts the structure, the policy framing and the source checklist, and marks every fact it cannot verify as to be confirmed. Enter your postcode to see which reports your site is likely to need.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.