Planning Permission Checker is built on one rule: a deterministic engine reads official data, and everything you see traces back to a named source. Nothing is scraped from listings, nothing is estimated by a language model, and where the data runs out we say so rather than rounding the corner.

The constraint check

Conservation-area and Article 4 boundaries are published as geometry by planning.data.gov.uk. We ingest each covered borough's polygons (refreshed monthly — the data changes slowly) and, when you enter a postcode, test its coordinates point-in-polygon against those boundaries in-process. The result names the designation and links the dataset. A point check is indicative: postcode centroids sit metres from front doors, and boundaries can run mid-street — near an edge, we say so, and the council's own map remains the legally definitive source.

Prices and comparables

Sold prices come straight from HM Land Registry Price Paid Data — real transactions, by postcode, with dates and tenure. Borough-level averages use the UK House Price Index. PPD carries no floor areas, so we never quote £/sqm from it; cost per square metre comes from real London project cost data instead, always as a low/expected/high range, never a single number.

Confidence tiers

Every major answer carries a tier. High: structured data matched to your location — a constraint boundary, a sold price. Medium: present but interpreted — cost ranges, uplift directions. Low: incomplete data or local judgement needed — flagged for manual review rather than papered over.

What the AI is allowed to do

A language model writes plain-English explanations of facts the engine has already established — that is its entire job. It is never permitted to invent constraints, approvals, prices, application references or legal conclusions, and its output must cite the source records it was given. If data is missing, it must say missing.

Expert review

The deterministic engine establishes the facts; the plain-English guidance is reviewed by a RICS-regulated chartered surveyor — Savas Bulduk MRICS, Director of Hampstead Chartered Surveyors & Building Consultancy (RICS Firm Reg. 923064). Where a project needs real professional input — listed building consent, a licence to alter, party wall matters or a feasibility review — your consented enquiry is sent to a RICS-regulated chartered surveyor (Hampstead Chartered Surveyors, Firm Reg. 923064) for paid advice. Some projects may also need drawings, planning consultancy, structural engineering, legal advice or other specialist input.

What we won't claim

Planning Permission Checker provides planning and cost intelligence for early feasibility only. It is not legal, planning, valuation, architectural, structural or surveying advice; planning outcomes are decided by local authorities, and every estimate here is a range to be verified by qualified professionals before you commit money. If a number on this site ever looks too precise to be honest, tell us.

planning.data.gov.uk	Conservation-area and Article 4 direction boundaries — official geometry, ingested per borough and refreshed monthly.
HM Land Registry Price Paid Data	Real sold-price transactions by postcode — the comparables behind every uplift discussion.
HM Land Registry UK House Price Index	Borough-level average prices, annual change and sales volumes on borough pages.
postcodes.io	Postcode and district geocoding — coordinates, borough, ward.
Real London project cost data	Build-cost data from real London projects — the calibration behind every cost range, always given as a low/expected/high range, never a single number.

How Planning Permission Checker knows what it knows