61 per cent of the studied coastline experienced a steepening over the last 113 years. The South of England showed the most dramatic changes, according to the research.

The more rapid landward retreat of the low water mark relative to the high water mark is the most alarming trend. This process can make waves much more damaging to the coast.

The narrowing and steepening of shorelines leads to an increase in the amount of wave energy hitting our sea defences. This can lead to structural damage and overtopping.

The study, published in the Royal Geographical Society's Geographical Journal, suggests that holding all defence structures in their current positions may not be sustainable in the long term. In some instances, as beach widths decrease and water depths increase in front of structures, they will no longer be able to offer the same levels of protection without further investment.

The narrowing of the coastline in the UK also has serious implications for conservation of important natural habitats, such as beaches, mudflats and salt marshes. In some locations, the area of such habitats is decreasing as the low water mark advances landward, but the high water mark remains fixed. This has implications for the species, such as birds, which use these areas for feeding or breeding.

One cause of steepening appears to be man-made infrastructure on the upper parts of shore, according to Dr Pontee. Infrastructure, such as sea walls and promenades, prevents the natural functioning of coastal environments. In natural conditions, unrestrained beaches and mudflats tend to move inland under rising sea levels and thus avoid steepening.

This can occur either under extreme storm events or as a slower and more gradual process in response to increasing water levels, according to Dr Pontee.

The interruption of the natural move inland is particularly marked on open coasts, where promenades and seawalls have been built across formerly wide sandy beaches; or in estuaries where low lying areas have been reclaimed for agriculture behind sea walls.

Commenting on the research, Dr Pontee said: 'These results have considerable implications for deciding on future coastal management options around not only the UK, but also potentially, the rest of the world. If we are not to spend increasingly large amounts of money on sea defences, we need to allow more room for coastlines to function as nature intended them to.'

The study is the first national study in the UK on coastal steepening. Over 1,000 locations in England and Wales were analysed.

The research team used data generated under the Department for the Environment, Food and Rural Affairs 'Futurecoast project' which analysed past coastal changes and present day coastal processes to make predictions about future changes in the position of the coast around England and Wales.