How Planning Permission Checker knows what it knows

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). That review applies to the guidance published here. It is not an individual assessment of your property, and no page on this site is a survey, a valuation or a planning decision.

Where the data stops and a professional starts

A dataset cannot draw a scheme, argue a case with a planning officer or inspect a wall. Where a project needs that, the site refers it to one of two independent practices and you choose which: design and consent work — drawings, planning applications, prior approval, lawful development certificates, appeals, listed building consent and Licence to Alter packages — goes to Hampstead Architecture and Planning (ARB-registered architects); condition, defects, party wall notices and awards, dilapidations and leasehold process go to Hampstead Chartered Surveyors (RICS-regulated, Firm Reg. 923064). Many jobs need both — the architects design and submit an extension, the surveyor serves the party wall notices — and some also need structural engineering, legal advice or other specialist input. Nothing on this site is sold; each practice quotes its own fees directly.

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.