The map, published last week, shows that the number of homes with a more than one in 1,000 risk of inundation has risen from a previous estimate of 1.9 million.
The main reason for the rise, equivalent to around one in ten of the total stock of residential buildings in England and Wales, is that the map's coverage extends to just over a third more rivers than previously.
The interactive map, which is able to focus on individual post codes, is mainly designed to help homeowners assess flood risk.
Environment Agency head of planning and local government Mark Southgate said that the map would also provide improved information for planning flood plain developments in line with PPG25.
London Thames Gateway Partnership environment officer Alex Nickson said the changes to the map within the London stretch of the South East's key growth area are "minor". He added that the partnership is about to embark on a strategic flood risk assessment in the Thames Gateway.
Meanwhile, Norfolk authorities are preparing to abandon hundreds of homes to the sea as part of a 100-year strategy for the county's coastline.
The Anglian Coastal Authorities Group shore management plan, due to go out to public consultation next month, recommends a policy of "managed retreat" for sections of its coastline. The authorities would concentrate sea defence efforts on selected stretches of coastline while allowing natural erosion to eat into others.
The Environment Agency's flood map can be viewed via www.PlanningResource.co.uk.