Lyme Regis is situated on an actively eroding stretch of the West Dorset coast and has, therefore, always faced considerable challenges from coastal erosion and landslipping. Although the earliest known coast protection structure, the Cobb, dates back to the 13th Century, many of the town's sea walls are relatively recent. Prior to the construction of these defences, the coastline would have been actively retreating in a similar way to the unprotected parts of the coast today, and there is strong historical evidence to indicate that a large part of the original mediaeval town has been lost to the sea.

Despite the existence of the coast protection structures, problems arising from coastal landsliding have been particularly serious during the 20th Century. Some twelve individual properties have been destroyed and many more severely damaged. There have been several major sea wall breaches along the main frontage, frequent substantial damage to roads and other infrastructure and the complete loss of the main coastal road to Charmouth. If no action is taken it is considered that, sooner or later, there will be further destructive failures. The Lyme Regis Environmental Improvements were initiated by West Dorset District Council in the early 1990s, with the principal aim of implementing engineering works to help ensure that the integrity of the town's coast protection is maintained in the long term and to reduce the damage and disruption coastal landsliding.

The construction work for Phase I, which comprises a new sea wall incorporating a sewage holding and pumping facility adjacent to the mouth of the River Lim, was completed in 1995. Since then, West Dorset District Council, with its principal consultants High-Point Rendel, have been carrying out a series of inter-disciplinary studies for the remaining areas of the town, in order to gain an understanding of the coastal system from the sub-tidal zone to the top of the coastal slope, particularly in terms of long-term coastline evolution. The purpose of the studies is to obtain information for use in the conceptual design of appropriate engineering schemes to ensure the long-term integrity of coast protection in the town. The principal findings of the studies to date are as follows:

• In the 18th Century, there was once a substantial continuous beach along the whole of the Lyme Regis frontage. The beaches are in long-term decline and are now a small fraction of their original volume. The decline is part of a natural process of fragmentation of the beaches along the West Dorset coastline which has been exacerbated and complicated by the building of structures such as the Cobb and the sea walls. There is no longer any natural supply of beach-forming shingle.
• The seabed and shore platform in front of the sea walls have undergone considerable erosion and lowering over the last two centuries, such that the sea walls' exposure to wave attack has increased.
• There has been a gradual long-term deterioration in the condition of the existing coast protection structures, some of which are now seriously undermined at their foundations.
• The connection of the Cobb to the mainland in the 1750s has resulted in the interruption of the west to east longshore drift and the substantial build-up of Monmouth Beach on its western side. The growth of Monmouth Beach at the Cobb has been at the expense of the western end of the beach.
• Limestone quarrying in the 19th Century accelerated cliff and foreshore erosion.
• Landslide systems extend over a kilometre in-land from the high water mark and consist of numerous interrelated elements and different landslide mechanisms.
• The landslides have formed as a result of marine erosion prior to the construction of the coastal defences causing the reactivation of ancient landslide systems. In addition, first-time failures are developed on the lower coastal slopes.
• The basal shear surfaces of the principal landslide units occur above particular marker beds within the Lias, which impose strong control on the landslides and give rise to a bench-scarp morphology. The Lias strata have a gentle dip to the south-east, facilitating the seaward movement of landslide blocks.
• Stability analyses indicate that many of the landslides are at, or close to, failure and ground instrumentation has confirmed continuing wide-spread movement over most parts of the landslide systems.
• The eastern part of Lyme Regis may be under threat from the continuing long-term westwards expansion of the Spittles/Black Ven landslide system.

The coast protection works, when implemented, are likely to comprise a combination of slope drainage and strengthening, for example using piles or ground anchors, the strengthening and refurbishment of existing sea walls and provision of new foreshore structures in order to hold a replenished beach.