Work to conserve a world-famous geological site will begin next week.

But a footpath used by ramblers and geologists to access the cliff-face in Brighton will remain closed indefinitely.

Brighton and Hove City Council closed Undercliff Walk in 2001 after chunks of the cliff fell behind the Asda superstore.

The council said the only way it could safely reopen the path was to secure the rock with bolts and attach steel mesh to catch falling debris.

English Nature objected, saying that would obscure a site with woolly rhino, wild horse and mammoth fossils.

The cliffs are a site of special scientific interest (SSSI).

A public inquiry was held last year when Deputy Prime Minister John Prescott granted planning permission to stabilise the rock but said mesh must not be used.

The council, English Nature and Brighton University specialists have carried out a study and agreed to trim and bolt some of the cliff but leave the fossil site untouched.

But without meshing it is still unsafe to open the path to the public, say council officers.

Phil Belden, chairman of the Brighton Urban Wildlife Group, which wants the path reopened, said: "This is mad. Why are they spending money to stabilise cliffs only to say they are not stable enough to open the path? It appears there is no public benefit in this work."

The council says the work is required to prevent major landslides and protect the seafront road.

Specialist contractor CJ Thorne will begin the work on Monday. Soil nails will be inserted into the cliff face and abseilers will be used for part of the job, which is expected to last 16 weeks.