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Basement Flash Flooding Campaign 2023

Flash Flooding. If you live in a basement property, you may be at a greater risk. Here is how you can prepare for flash floods.


This briefing updates members on the second year of the Basement Flash Flooding Campaign and provides an update on the actions undertaken by London Councils and partners following the floods of 12 and 25 July 2021.


On 12 and 25 July 2021, London experienced intense rainstorms that overwhelmed the drainage systems and led to extensive surface water and sewer flooding, affecting homes, businesses, health infrastructure and transport networks.  24 boroughs were impacted, with the worst impacts felt particularly in parts of east and north London.

Amongst the actions undertaken following the event, boroughs, together with the Environment Agency and other relevant partners established a Surface Water Strategy Group. The Group met for the first time in December 2022 and comprises representatives from the Environment Agency, The Greater London Authority, Transport for London, London Councils, Thames Water, the Thames Regional Flood and Coastal Committee and the London Fire Brigade. 

The strategic group is working together to deliver the following: 

  • The first pan-London strategy for surface water flood risk management in 2024. 
  • A communications and engagement plan to support the development and delivery of the strategy.
  • An action plan with detailed objectives for stakeholders.
  • A funding plan to support the development of the strategy, action plan, and communications plan.
  • An annual monitoring framework, which aims to ensure that lessons can be learned from the various reviews and reports carried out by since 2021. 

One of the key areas of concern highlighted was basement properties as flood risk is considered to be high but there is a lack of data concerning precise level of risk and location of properties as well as occupiers having a lack of understanding of the risk, the need to prepare and what to do in case of emergency.

As a first step, an informational campaign was sent out to properties in boroughs who were most at risk during the flooding season last year and will be repeated this year. The campaign is keen to build on Londoners’ awareness of the risk and the actions they can take, drawing on the experiences of the flash floods in summer 2021.

The campaign created key messages with input from multiple agencies and the boroughs and created an information leaflet (attached below). The leaflet will be sent out to around 45,000 properties via Royal Mail and is expected to land in homes from the 7th July 2023.

The campaign has focused on basement properties as those that are high risk from flash flooding events, although other addresses for properties that have basements (over more than one floor), such as maisonettes, have been included in the dataset.

The dataset has been compiled using a variety of sources and we are also working with others such as Age UK London to share copies of leaflets with local groups and other more vulnerable Londoners.

There is basement data for every London Borough. The greatest number of basements are in inner London boroughs. The top five by numbers are Kensington & Chelsea, Islington, Westminster, Hammersmith & Fulham and Hackney.


This campaign represents an initial step towards improving public awareness of the risks of surface water flooding. The work of the different organisations with responsibility for flooding after the events in 2021 have highlighted profound weaknesses regarding London’s approach to surface water flooding. The Surface Water Strategy Group has formed to help address this and one of the first tasks was to recruit consultants to design a comprehensive strategy for surface water flooding for London.

Engagement by officers within both the UK and internationally has shown that successful management of surface water flooding is frequently a long-term multi-decadal project, requiring strong on-going political and public support as well as the identification and implementation of significant resource. As London moves towards a warmer future, flooding events such as those seen in July 2021 will become more frequent and severe.

London Councils climate change polling has demonstrated that Londoners are both extremely concerned about climate change but are also willing to act both to mitigate and adapt. Utilising this public support will be key to successful long-term management of surface water flooding.


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