The Mississippi River, which used to sweep up dirt in one stretch of the delta only to deposit it in another, has now been channelled, for flood-prevention, to wash the land into the sea.

Faced with demands for larger deposits only three mortgage lenders now offer deals to people with a 5% deposit, while one in four mortgage products require a deposit of 40% or more.

To make up for the lost revenue, banks will need to improve their deposit margins by only 0.3 percentage points, Mr Meleis calculates.