A public inquiry was due to open on Tuesday into the proposals by Brighton and Hove City Council to cover the cliff face at Black Rock, Brighton, with wire mesh.

The council said the work was needed to make the area safe after rock falls on to a footpath below the cliffs.

But English Nature has raised concerns over the loss of access to fossils of mammoths and woolly rhinos still preserved in the rock.

They tell us the story of a time when woolly mammoths and rhinos roamed round what is now the seashore at Brighton Tony Cosgrove, English Nature

The cliffs were one of the first Sites of Special Scientific Interest in Britain; designated in 1951.

An English Nature spokesman said the 200-metre stretch was "a unique and irreplaceable feature of outstanding national importance".

The group has called for the council to divert the footpath through the marina rather than "seriously damage" the scientific value of the cliffs by obscuring them with mesh.

Tony Cosgrove, of English Nature, said: "The cliffs here at Black Rock are a bit of a snapshot in time.

"They tell us the story of a time when woolly mammoths and rhinos roamed round what is now the seashore at Brighton.

Cliff instability

"It's a really interesting piece of geological history because it tells us about climate change and helps us plan for future climate change which might affect this area."

A spokesman for Brighton and Hove City Council said it had consulted English Nature before applying for planning permission and had modified its plans to have less impact.

Councillor Gill Mitchell, chairwoman of the council's environment committee, said: "The council recognises the national geological importance of the site.

"We believe that the application proposals represent a necessary compromise, as they address the conservation interest and the effects of cliff instability."

She said the work would ensure the safety of Black Rock and improve access for scientific study of the cliffs.