Concerns are being raised about the use of a synthetic rubber, best known for its use as wetsuit fabric, in the construction of Dawlish's new sea wall.

Closed-cell neoprene has been used as a kind of grouting between the joints in the wall panels – but pieces of it have been washed out by the sea.

The campaign group Save Teignmouth and Holcombe Beach has flagged up the problem in posts on its Facebook page.

The group have always maintained that the £80 million sea wall is not the best way to protect the railway line from high tides, arguing that breakwaters should be incorporated, to reduce wave energy.

A statement on its Facebook page about the dislodged neoprene reads: "We ask the question: is it fit for purpose?

"Whilst I have come across this used in inland waterway infrastructure, the fact that it's coming out so soon shows that this sports clothing material has limits as to what purpose it can satisfy.

"Rocks & neoprene ripped up by waves are being thrown up very close to the track on the path, and this is before the more serious storm season begins - another sign that breakwaters should have been incorporated into the coast protection plan instead of over-engineering this wall at massive cost.

"Questions remain about drainage issues as well. We hope lessons can be learnt from this experience."

What do Network Rail say about it?

Network Rail, responsible for the design and construction of the sea wall project, said it is aware of the neoprene problem.

In a statement the company said: "The black foam-like material that can be seen between the panels of the new sea wall at Dawlish is called expanded closed-cell neoprene and has been applied to the joints between the wall panels to initially maintain structural integrity of the new wall and in the long term, prevent beach material getting into the joints and protect the wall against movement due to changes in temperature.

"Network Rail is aware that some of the neoprene has become dislodged and is working with our contractor to repair it."