Crumbling cliffs dating back to the Ice Age will remain on public view despite approval for a major scheme to renovate the coastline.

Conservationists had feared Brighton and Hove City Council's £500,000 programme to preserve the cliffs at Black Rock, Brighton, would actually cause severe damage.

But Deputy Prime Minister John Prescott has insisted on a series of strict conditions for the work to go ahead. These include forcing the council to drop plans to mask the cliffs with mesh.

The verdict followed a public inquiry into the scheme, drawn up to prevent repeats of cliff falls which forced workers and shoppers to flee the Asda store at Brighton Marina in April 2001.

English Nature and the Brighton Urban Wildlife Group welcomed the restraints but there was also disappointment Mr Prescott blocked the reopening of 200 metres of Undercliff Walk closed after the slip.

The proposals were to drive bolts into the rock face and obscure 200 metres of cliffs with mesh to prevent loose fragments of rock plummeting on to the public path below.

Conservationists and geologists value the stretch of cliffs, part of a site of special scientific interest (SSSI) on the coast between Brighton and Newhaven.

A sea of sludge poured off the hills as the last ice age ended, forming the cliffs as it covered the ancient coast with rock, mud and parts of mammoths, including teeth and tusks.

Public inquiry inspector Alison Moore, whose report was approved by Mr Prescott, called the area "an important geological site" which could be stabilised without the need for mesh, which would "obscure the features".

She rejected Brighton Urban Wildlife Group's call to let the cliffs decay naturally and said the marina and A259 South Coast Road needed protection.

English Nature conservation officer Jon Curson said: "This decision is the best solution for both nature conservation and the people of Brighton and Hove.

"It will help protect the future of the marina access road and allow generations of geologists to study the unique history of this place."

Phil Belden, chairman of the Brighton Urban Wildlife Group, was baffled by the decision to keep Undercliff Walk closed.

He said: "If it's not safe to walk along that part of the cliff face, then how is it safe to walk along any other part from Brighton to Newhaven?

"But our biggest concern was the meshing, which would have completely ruined the extremely important chalk cliffs which are classic emblems of England."