City of Westminster Flood Risk

April 2022

The City of Westminster adopted their City Plan 2019-2040 in April 2021. The strategic vision for the City is that:

“Sustainability must drive everything we do. This strategy defines what we need to achieve and how innovative planning and design will achieve it. Greener living must inform the choices we make – sometimes literally. Soft landscaping and streets lined with trees, bring natural beauty and mitigate against the harmful effects of CO2. A stunning city encourages walking and cycling, bringing further environmental benefits”.

What is Policy 35?

Policy 35 relates to flood risk and sustainable drainage within the City of Westminster. Over 10 separate statements form Policy 35 and it sets out a clear strategy for dealing with flood risk and sustainable drainage throughout the City.

A. All developments should be safe for their lifetime from the risk of flooding, complying with the council’s Strategic Flood Risk Assessment (SFRA), Surface Water Management Plan (SWMP), Local Flood Risk Management Strategy (LFRMS) and the Mayor of London’s Regional Flood Risk Appraisal (RFRA).

B. A site-specific Flood Risk Assessment (FRA) must be submitted for: 1. developments of 1 hectare or greater; 2. all developments in Flood Zones 2 and 3; and 3. all developments within a Surface Water Flood Risk Hotspot.


C. Highly Vulnerable Uses will not be allowed within Flood Zone 3; in Flood Zone 2 they will be required to pass the Exception Test and should as far as possible be located outside of the Surface Water Flood Risk Hotspots.

D. Proposals for Essential Infrastructure and More Vulnerable Uses within Flood Zone 3 will be required to pass the Exception Test. Within the Rapid Inundation Zone, basement dwellings and basement extensions to existing dwellings will not be acceptable.

E. More Vulnerable Uses should, as far as possible, be directed away from Surface Water Flood Risk Hotspots.

F. A Flood Warning and Evacuation Plan will generally be required for More Vulnerable Uses within the areas at risk of tidal breach flooding, especially if the land use is within the Rapid Inundation Zone.


G. All existing flood management infrastructure will be protected, including access for maintenance. Wherever possible, an undeveloped buffer zone of 16m should be maintained around flood defence structures, including buried elements of the flood defence.

H. Improvements to flood defences will be secured through planning conditions and / or legal agreements where the size, type and / or location of development impacts on flood risk. Development should not limit future raising of flood defences outlined in the Thames Estuary 2100 Plan.

I. Where appropriate, planning permission for developments which result in the need for off-site upgrades to the water or sewerage network, will be subject to conditions to ensure the occupation is aligned with the delivery of necessary infrastructure upgrades.


J. New development must incorporate Sustainable Drainage Systems (SuDS) to alleviate and manage surface water flood risk. Development should aim to achieve greenfield run-off rates and demonstrate how all opportunities to minimise site run-off have been taken.

How does Policy 35 affect my development?

The Westminster policy guidance is quite prescriptive in its’ application, but in essence it seeks to sequentially locate development within the City away from flood zones and surface water hotspots in line the the NPPF. However, there is a tacit acknowledgement that, given the density of buildings, that this is not always possible.

All developers should engage early with Westminster to understand whether a SuDS statement will be required as part of submission in accordance with the London Drainage Hierarchy (or with any Major Development). Developers seeking to undertake basement expansions or extensions should also be aware of the policies relating to Rapid Inundation Zones from the River Thames.

Westminster SPD

The borough of Westminster has also published a consultation draft of a supplementary planning document in May 2021 that has yet to be adopted. The SPD contains useful contextual information and specific policies that would need to be complied with, if adopte:

  • London Plan

  • Policy SI 12 Flood Risk Management

  • Policy SI 13 SuDS

  • Mayor of London’s Regional Flood Risk Appraisal

  • City Plan Policy 35 on Flood Risk – site-specific Flood Risk Assessments (FRAs) will need to be prepared by prospective developers for specific development sites. These sites are the following:

  • Development of more than 1 hectare

  • Development in Flood Zone 2 and 3 including minor development and change of use

  • All developments within a Surface Water Flood Risk Hotspot

  • City Plan Policy 45 on Basement Developments – requires that A site-specific Flood Risk Assessment (FRA) and a structural statement will be required for basement developments located in flood zone 2 or 3, or surface water flood risk hotspots.

Flood Risk Assessments by Aegaea

Aegaea hold all fluvial and tidal models and data for the City of London and City of Westminster that enable us to analyze rapid inundation zones, flood zones, inundation areas and levels without having to wait for data requests from the EA or local authorities. Given the building density and the fact that there are 15 critical drainage areas identified in the SWMP, consultation early and engagement of professional advice on flood risk in Westminster is essential.

We have successfully delivered flood risk assessments across Westminster for a variety of clients, so get in touch with one of our consultants and see how Aegaea can offer you professional, expert advice.

Request your free, expert quote now

Aegaea work alongside home owners, private developers, planning consultants, architects, local authorities, international development agencies and contractors. Aegaea know exactly how to help you.

Upload File(s)