The Environment Agency is urging people to check if they are at risk of flooding - 60 years after floods devastated parts of the UK.
An area the size of Kent was damaged during the 1947 floods
The public can check their risk using flood maps on the agency's website.
In March 1947, heavy rain swept across Britain causing major rivers to burst their banks in the south, Midlands, East Anglia and North Yorkshire.
Agency Chief Executive Dame Barbara Young said people at risk can sign up for free phone or fax flood warnings.
These are provided by the Floodline Warnings Direct service.
"Although floods on the scale of 1947 are rare, history shows they do happen and we encourage people to look at our flood map on the Environment Agency website to find out whether you live in an area that could flood from rivers or the sea," she said.
Around 4.5m people in England and Wales are at risk from flooding, the agency warns.
There are more than 2.3m properties in areas that could flood due to building in flood plains.
Heavy rain caused rivers to break their banks
Dame Barbara said: "We want everyone to understand that if you could be affected by flooding you should take action now to prepare.
"Have a flood plan in place so you know what needs to be done in the event of a flood."
The expected damage from floods in England and Wales had already reached £1.4bn a year on average, she said.
She cited the location of new development as the "single most important factor" to avoid flood risk increasing, followed by the layout and design of development on a site.
"Getting these three essential aspects right means that planning authorities can avoid increasing the number of lives at risk and contribute greatly to reducing flood risk," she said.
In 1947 an area of almost 300,000 hectares was damaged, at a cost estimated at £12m, equal to around £300m today.
The Met Office said weeks of frost had left the ground "frozen hard" meaning rain and meltwater could not soak into it. By the evening of 11 March, 1947, vast areas of southern England were under water.
As warm weather spread northwards and eastwards, meltwater from the Welsh mountains poured into the valleys of the Severn and Wyre, causing flooding in Herefordshire and Gloucestershire.
Rain and severe gales caused by a deepening depression from the Atlantic on 15 March worsened the situation as the flooding spread across the country, it said.