However, it skirts the top of 70m high chalk cliffs, and some 140 years of coastal erosion has seen the cliff recede to within 10m of the highway at two locations on Afton Down.

The local authority initially considered moving the road, but the idea was eventually rejected, partly because it is an important tourist attraction.

High-Point Rendel was appointed to carry out a preliminary assessment of stability options for the highway and subsequently started work on the 'preferred solution', an anchored bored pile retaining structure that will be constructed entirely within the width of the existing highway.

This feature has been designed in such a way that it will stabilise the road while cliff recession continues naturally and to become exposed up to a maximum height of 10m at the end of its serviceable life, at which time the road will partly pass over a cantilevered section above the cliff.

Apart from ensuring that the entire structure could be easily decommissioned at the end of its natural life, High-Point Rendel also had to take into account the fact that the cliffs form a Site of Special Scientific Interest (SSSI) and are a candidate for designation as a Special Area of Conservation (SAC).

Finalising the design thus included a detailed site investigation and the production of an Environmental Statement to allow for assessment under the Habitats Regulations.