Drainage and SuDS planning conditions by London borough: which councils condition most

Every London borough we have read deeply, ranked by how often an approval carries a drainage or SuDS condition, with pre-commencement share, discharge outcomes and the number of notices behind each row.

Trails Research·Updated 2026-09-10·4 min read
From our ongoing reading of London planning decision notices
…heaviest borough conditioning share
…lightest borough conditioning share
…London-wide conditioning share

The borough range appears once enough boroughs have been read past the publication bar.

The same drainage submission does not face the same odds in every London borough. This page ranks the boroughs we have read most deeply by how often an approval carries a drainage or SuDS condition, and puts the figures that shape a programme beside it: how many of those conditions must be discharged before work starts, and how discharge submissions fare. Every row states how many decision notices sit behind it.

Which London boroughs attach drainage and SuDS conditions most often?

The table appears once enough boroughs have been read past the publication bar of 300 notices each.

What the spread means for a submission

The conditioning share and the pre-commencement column are different questions. A borough that conditions rarely but attaches a pre-commencement condition to most of the approvals it does condition can hold up more start dates than one that conditions everything and lets most of it close later. Read the two columns together, and follow the borough link for the condition themes and refusal grounds behind each row.

Why this comparison is published now

A ranked table is only honest when the reading behind each row is deep enough that the differences are the boroughs' and not ours. We held this page back for that reason. Every borough listed now has at least 300 notices behind its figures.

Where does this come from?

Every figure is computed from planning decision notices we read across London boroughs, recomputed every morning as more are read. A rate is published only when its own sample clears a floor; where it does not, the cell says so rather than showing a number that would not survive the next fortnight of reading. Only aggregate figures appear here: never a scheme address, an application reference, or condition wording. See the methodology page or the London-wide picture.

This is the free, public view. Flood and drainage consultants use Trails to see the same table at scheme level: which live applications in each borough carry a drainage condition, and the architect behind each one.

See how Trails works for consultants →

Frequently asked questions

Which London boroughs attach drainage or SuDS conditions most often?
The table on this page ranks every borough we have read past our publication bar by the share of approvals carrying a drainage or SuDS condition, recomputed daily. The spread is wide: the heaviest borough conditions a multiple of the lightest, so the London-wide share describes almost nobody’s borough. Each row links to the borough page with the condition themes and refusal grounds behind the figure.
Why do some boroughs show no discharge refusal rate?
A discharge refusal rate is published only when the borough has at least twenty drainage discharge-of-condition submissions in the window. Below that, one or two decisions would swing the percentage, so the cell says the sample is too small rather than showing a number that would not survive the next fortnight of reading. The same floor applies to the pre-commencement share.
Why are some London boroughs missing from the comparison?
A borough is listed once we have read at least three hundred of its planning decision notices in the trailing window, so that the differences in the table are differences between authorities rather than differences in how much we have read. Boroughs below that bar are named under the table and join it as our reading deepens. The window rolls, so the table moves as authorities change their practice, not only as we read more.

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 →