The figures for properties in England identified as being at significant risk of flooding (defined as a probability of flooding in any one year greater than 1.3 per cent. or one in 75) from the Environment Agency's national flood risk assessments are:
2003: no assessment undertaken;
2004: 315,000 properties, with subsequent analysis indicating that approximately 285,000 were residential;
2005: 517,000 properties, but the assessment did not differentiate between residential and commercial;
2006: 469,000 properties of which approximately 393,000 are residential.
I would like to take this opportunity to clarify my answer of 28 February 2007, Official Report, column 1328W, in which the figure for the 2004 assessment of properties at significant risk related to residential properties only, while all other figures related to residential and commercial properties.
It should also be noted that the differences between assessments are almost entirely due to changes in data and analysis techniques as opposed to the actual flood risk, for example the number of properties within the floodplain for which no result is available has fallen dramatically from 265,000 in 2004 to 28,000 in 2006. This represents an improvement in the analysis but leads to a commensurate increase in the number of properties in each risk band