In seven London boroughs, applications within conservation areas are approved at rates 10 or more percentage points higher than those outside. Only four boroughs show the expected penalty. The conventional wisdom that conservation areas make planning harder is wrong in most of London.
Does conservation area status help or hinder small site approval?
Ask any small site developer about conservation areas and you will hear the same thing: harder to get consent, longer determination, more expensive design work. It is one of those industry assumptions that everybody repeats and nobody checks. So we checked it, across 15,114 applications in 33 London boroughs over three years.
Seven boroughs show a CA advantage; only four show a penalty
In seven boroughs, applications within conservation areas are approved at rates 10 or more percentage points higher than those outside. Not marginally. Materially.
Camden leads the list. Conservation area schemes are approved at 85.4% (n=164). Schemes outside conservation areas: 55.3% (n=76). That is a 30.1 percentage point difference in favour of the heritage-protected site.
Brent follows a similar pattern: 64.1% in conservation areas (n=117) against 42.8% outside (n=505). A 21.3 percentage point gap. Merton: 79.2% inside (n=48) versus 58.5% outside (n=272), a 20.7 point difference. Westminster: 84.6% (n=299) versus 68.9% (n=90), a 15.7 point spread. Hackney: 72.1% (n=43) versus 59.4% (n=101), 12.7 points. Hounslow: 57.5% (n=87) versus 46.1% (n=258), 11.3 points.
Only four boroughs show the expected penalty by more than 10 percentage points: Southwark at -12.3pp, Hillingdon at -11.4pp, Kingston at -10.4pp, and Richmond at -10.0pp. Four boroughs. Out of thirty-three.
| Borough | In CA | Outside CA | Difference |
|---|---|---|---|
| Camden | 85.4% | 55.3% | +30.1pp |
| Brent | 64.1% | 42.8% | +21.3pp |
| Merton | 79.2% | 58.5% | +20.7pp |
| Westminster | 84.6% | 68.9% | +15.7pp |
| Hackney | 72.1% | 59.4% | +12.7pp |
| Hounslow | 57.5% | 46.1% | +11.3pp |
| ... | |||
| Richmond | — | — | -10.0pp |
| Kingston | — | — | -10.4pp |
| Hillingdon | — | — | -11.4pp |
| Southwark | — | — | -12.3pp |
The remaining boroughs cluster around zero — conservation area status makes no statistically meaningful difference to the outcome.
This is not what the industry expects. The conventional wisdom runs roughly as follows: conservation areas mean additional scrutiny, heritage officers, restricted materials, constrained massing, and a higher likelihood of refusal. The data says the opposite is true more often than not.
The most likely explanation is self-selection. Developers and their architects are not choosing conservation area sites at random. They are choosing them knowing the constraints, investing more in design quality to meet the higher bar, engaging more thoroughly at pre-application stage, and submitting schemes that are — on average — better prepared than those outside conservation areas. The conservation area is not making approval easier. The type of applicant drawn to conservation area sites is producing better schemes.
There may also be a design code effect. Conservation areas have established character — materials palettes, scale, massing, roofline patterns. That legibility works in both directions. It constrains what you can do, but it also clarifies what you should do. A developer working within a well-defined conservation area character has a clearer design target than one working on a street with no discernible identity.
Stop filtering out conservation area acquisition targets
Take a practical case. A developer is comparing two sites in Brent. One is a Victorian semi in the Mapesbury conservation area. The other is a similar property half a mile north, outside any designation. Both could accommodate a conversion to 3 flats. The conservation area site will cost more in design fees — a heritage statement, higher-quality materials, possibly a pre-application meeting with the conservation officer.
The Mapesbury site sits in a borough where conservation area conversions are approved at 64.1%. The non-designated site: 42.8%. That is a 21 percentage point gap.
Assume the additional design and heritage costs for the conservation area scheme run to £8,000–£12,000 above the standard submission. Against a scheme with a gross development value of, say, £1.2 million, that is less than 1% of GDV. For a 21 percentage point improvement in the likelihood of getting consent, it is not a close call.
The practical takeaway is not that conservation areas are easy. They require more care, more investment in design, and a willingness to work within constraints. The takeaway is that developers who automatically filter out conservation area sites from their acquisition searches are discounting opportunities that, statistically, perform better than the alternatives. At least in these seven boroughs.
Whether that holds in Southwark, Hillingdon, Kingston, or Richmond — where the penalty is real — depends on the specific area and the nature of the constraint. Conservation areas are not uniform. Some protect grand Victorian set-pieces. Others protect suburban cul-de-sacs. The label is the same; the planning reality is not.
Why self-selection makes causation unprovable
This is associative, not causal. The data shows that conservation area applications have higher approval rates in certain boroughs. It does not prove that conservation area status caused those approvals. Self-selection is the most plausible confound — and it cannot be controlled for in observational data of this kind. Sample sizes for the conservation area group are small in some boroughs (Barnet: n=18), so individual borough figures should be treated with appropriate caution. The analysis also does not distinguish between different types of conservation area or different levels of heritage sensitivity within them.
Borough-level conservation area analysis, including area-by-area breakdowns and site type interactions, is covered in the full intelligence reports.