I think climate change is responsible for much of the flooding (though I have seen it suggested that it is all a conspiracy and a myth): there's simply been a lot more of it than there used to be, which suggests more and different planning will be needed in future years than in the past. It might be an idea to stop building on floodplains (is John Prescott still going ahead with his Thames Gateway dwelling-in-a-lake scheme?) and to lean on insurance companies to offer proper cover to those who are already stuck there.
But there's also been a huge shift away from Britain being an agricultural economy, as you suggest. I don't know how much of a role this plays. It's the flooding in towns that causes the human problems. Do you think better management of farmland might alleviate it? You could be right, I don't know.