ThamesWeb's Flood Defence page provides a comprehensive overview of the situation facing a large chunk of the English population. The copy below was on the site before this summer's major flooding.
The area at risk from flooding across the Thames is home to over a million residents and workers, 500,000 properties, 38 Underground and DLR stations, and City Airport, as well as many areas recognised for their ecological importance. An estimated 75% of the property value at risk from tidal floods in England and Wales lies within the Thames tidal flood plain. A large-scale flood event in this area would have disastrous effects, causing millions of pounds worth of damage to businesses, homes and infrastructure, and potentially causing the loss of life for thousands of London's residents.The page includes descriptions of the government and administrative structure that must coordinate in any flood defense effort, photos of the Flood of '53 and the great gates of the Thames Barrier (designed to protect London until 2030), a map of the flood defense area:
and a chart showing how frequently the Barrier gates have been closed for flood protection in the years 1983 - 2003: