National EPC advice is written for the national housing stock — mostly post-war, mostly cavity-walled, mostly whole houses. London is none of those things, which is why so much of that advice lands badly here.

1. The 1920 line

There is a rough dividing year in British construction: around 1920. Before it, walls are typically solid nine-inch brick with no cavity. After it, cavity construction becomes normal.

Most of inner London sits on the wrong side of that line. Which means the single most-recommended improvement in every generic article — cavity wall insulation — is simply unavailable. The measures that actually move a solid-walled London terrace are loft insulation, heating and controls, glazing, and occasionally internal wall insulation, which is expensive and eats room space.

Head a few miles out and it flips. The interwar suburbs are cavity built, and filling them is genuinely one of the best-value improvements available. Knowing which side your home sits on tells you more than any online estimate.

2. Conversions change everything

London subdivided its housing more than anywhere else in the country. A converted flat is not half a house, and it is not assessed as one.

Only surfaces facing the outside — or an unheated space — count as losing heat. A middle-floor flat with heated homes above, below and either side loses heat through very little, and frequently rates a full band better than the top-floor flat in the same building, which carries the whole roof.

Getting that mapping wrong — a party wall recorded as an external one — produces a certificate that is simply incorrect, and it is the most common reason a London EPC has to be re-lodged. It is also why a twenty-minute visit is a false economy in a converted property.

3. Conservation areas narrow the options

Large parts of London are conservation area, and plenty of individual buildings are listed. That routinely rules out the two improvements a generic report leads with: replacement windows and external wall insulation.

What remains is real but narrower — secondary glazing, loft insulation, draught-proofing the existing sashes, heating controls. A recommendation report that suggests work planning will never permit is not much use to you, which is why local knowledge matters more here than the software does.

What this means practically

Two homes on the same street, built the same year, can rate a band apart because one is a whole house and one is a middle flat. Neither owner did anything different. Before spending money on the basis of a generic list, find out which of these three factors is actually binding on your property.

We have written up what this means area by area for East London and South London, down to the housing stock in individual postcodes.