The practices behind basement work, by London borough: how concentrated it is

How many architecture practices generate the basement applications in each London borough, and what share of that work the five and ten most active hold. Counts only; nobody is named.

Trails Research·Updated 2026-09-14·4 min read
From our ongoing reading of London planning applications
…basement applications with their practice read so far, of 0 in the window
…distinct practices identified so far across those applications
…boroughs with half or more of their basement work read, where concentration is published

Counts only. The practices are visible inside the product to the firms that use it; on this page nobody is named. Concentration appears for a borough once half of its basement applications have had their practice read; until then the row shows how far the reading has got.

Structural engineers win basement work through architects, and in most London boroughs a surprisingly small number of practices generate most of it. This page counts the practices named on basement applications in each borough and reports how concentrated that work is: what share the five most active hold, and the ten. It is the map of who to know, drawn from public planning records and refreshed every morning.

How concentrated is basement work in each borough?

The table appears once enough basement applications with a named practice have been read in each borough.

What the numbers mean for an engineer

Concentration is the number that decides the strategy. A concentrated borough rewards depth: a handful of standing relationships, kept warm, cover most of the pipeline. A dispersed borough rewards reach: the approach has to be triggered by each scheme as it appears, because no short list of practices covers it. Trails is built for both, but the table tells you which one your borough is.

Where does this come from?

Practices are read from the planning applications themselves: the drawings and statements name the practice that produced them. We match basement schemes by their proposal description across the London boroughs we cover, resolve each practice to one name across its spelling variants, and count. Shares are published only where at least 20 applications name a practice. No practice, scheme or address is named on this page. See the methodology page or the basement conditions by borough.

This is the free, public view. Structural engineers use Trails to see which practices those are, the basement schemes each one has live, and who they already know there.

See how Trails works for structural engineers →

Frequently asked questions

Why are the practices not named?
Because the page is a map of concentration, not a lead list. It tells a structural engineer whether a borough rewards a few deep relationships or a wider net, using counts read from public planning records. The practices themselves, their live schemes and who you already know there are visible inside Trails to the firms that use it.
What does the share held by the five most active practices mean?
Of every pairing between a basement application and a practice named on it, the share belonging to the five practices with the most applications in that borough. A high share means a handful of practices generate most of the basement work; a low share means the work is spread widely. The live figures are on this page, per borough, refreshed daily.
Which boroughs are covered?
The London boroughs where Trails reads planning records, listed once at least twenty basement applications in the window name a practice. Boroughs below that bar join the table as reading deepens. The window rolls, so the table moves as practices win and lose work, not only as more is read.

About this data

This article reports patterns in UK planning decision notices that Trails reads across London local planning authorities, recomputed daily. Every figure carries its own sample, and the London page shows how much of each borough's decisions we have read.

→ The full London flood & drainage picture→ Methodology and sources

About Trails

Trails reads London planning decision notices every morning and shows flood and drainage consultants which schemes have just picked up a drainage condition, which discharge submissions were refused, and the architect behind each one.

See how Trails works for consultants →