Speaking at the Labour Party conference in Manchester, secretary Benn said that climate change was moving the goal posts on what parts of the country needed to be defended and how.
"We will need to invest more in coastal and flood defences," said Benn.
"We have already increased the budget by £200M, but will need to do more in the future.
"If we cannot defend, we will have to adapt and people in areas that cannot adapt will have to move."
Benn added that communities, farmers and local authorities would increasingly be required take over the maintenance of defences from the Environment Agency.
However, Acting Agency chief executive Paul Leinster added that communities would only be able to protect themselves if their proposals fitted in with the Agency’s strategic goals.
"If somebody is going to take over the protection of defences, we have to give them permission for that to happen," said Leinster.
"The coast is a living thing. If we withdraw from maintenance, the body [wanting to take it over] would have to come to us for permission to continue maintaining the defence, and in some cases we will say no. You can’t take somebody else’s flood plain."
While all seem to agree that sea level rises are inevitable, final rises were far from certain, said Leinster.
"People think there are technical fixes for everything," he said.
"But as climate continues to change, the impact will be felt into the future. People will move."
Professor of urban water at Sheffield University Richard Ashley told NCE that Benn admitting the Government could no longer centrally fund the maintenance of all defences made a lot more sense than telling people that they would be protected come what may.
"The Government needs to get honest about what can and can't be done," said Ashley.
"The Government needs to help people and communities to develop the capacity to be self-reliant in terms of flood risk management.
"We seem to be moving in the right direction but this is only the start and more realistically targeted money from central government for the local authorities is crucial."
He added that many in the engineering were still too wedded to the notion of "lumps of concrete" as a panacea to flood risk management.