Remedial work will have to take place at Arcow Quarry to prevent up to 250,000 cubic metres of rock tumbling to the bottom of the site.

Tarmac Northern Limted, which owns the quarry near Helwith Bridge, is seeking planning permission to extend its workings to the west of the existing site.

The application will be heard by the Yorkshire Dales National Park Authority planning committee on Tuesday.

A report to the meeting reveals that in 2001 Tarmac appointed consultants to look at stabilisation works for rock faces within the quarry.

"A series of tension cracks has developed progressively in the ground above the western faces and these have now reached the limestone scar close to the land ownership boundary at the western edge of the quarry," says the report.

The consultants conclude that there is a potential for a massive single rock slide but the probability of this occurring is low.

"However because of the potentially serious consequences of such an event, remedial work should be given high priority," the report adds.

The planned work would include excavation beyond the existing western boundary into the Ingleborough Site of Special Scientific Interest and Special Area of Conservation.

Planning members will hear that concerns have been raised about how the extension will affect the flow of traffic through Settle.

All the stone from Arcow is transported by road, with most heading for the company's own asphalt plants at Skipton, Leeds, Sandside in Cumbria, Clitheroe and Agecroft in Manchester.

Virtually all of the quarry's 104 lorries travel south down the B6479 from Helwith Bridge to Settle and 85 per cent then travel through Settle town centre to reach the A65.

The current operating and transporting hours of the quarry are 6am until 5pm on weekdays and 6am until noon on Saturdays. "It is assumed that if consent was granted, members would wish to see more limited hours," said the officers' report.

Members are being recommended to arrange a second site visit before making a decision

o The Secretary of State has decided not to intervene in a decision to approve a four-year extension of work at nearby Dry Rigg Quarry.

National park members gave the go-ahead in April after hearing the extension would ensure the continuation of the quarry's £1 million a year input into the local economy. Their decision went against the advice of planning officers.

However, in a letter to the national park, Denis Spooner, from the minerals and waste planning division of the Office of the Deputy Prime Minister, said the Secretary of State would not be calling in the application.

"He has concluded that intervention would not be justified as there is not sufficient potential conflict with national planning policies, or any other sufficient reason, to warrant calling in the application for his own determination. The present application will only have a localised impact.

"He has therefore decided that he should leave the decision on whether or not to grant planning permission to the national park."