A TV archaeologist criticised a county council today over the destruction of the landscape around one of Britain's top prehistoric sites.

Thornborough Henges, near Ripon, has the greatest concentration of late Neolithic and early Bronze Age sites in the country.

It represents the largest prehistoric quarrying operation in Britain and construction firm Tarmac has proposed extending its activities in the area.

Dr Mark Horton, a presenter on the BBC's Time Flyers programme, criticised North Yorkshire County Council over the destruction of the landscape around the site.

Dr Horton, head of archaeology at the University of Bristol, said: ''I've been appalled by what I've seen at Thornborough. Archaeological sites like this should be protected and plans such as these shouldn't even be proposed.

''That such landscape destruction could even be considered around Stonehenge, or even our lesser-known sites in the south, is unthinkable. ''Yet at Thornborough, it is OK to seriously consider the total loss of a prehistoric landscape, arguably as important, for simple economic gain.''

North Yorkshire County Council permitted Tarmac to quarry in the area in 1994 with ''only a very limited archaeological survey'', Dr Horton said. Nosterfield Quarry in Thornborough is one of the county's most important quarries, producing more than 500,000 tonnes of sand and gravel each year, but supplies from the existing reserves are expected to run out within three years.

But Dr Horton said plans for a ''massive expansion'' of gravel quarrying would effectively isolate the village of Nosterfield and the henges.

No formal planning application has been submitted to the council, but Tarmac's proposals have met fierce local opposition from residents, who have established the Friends of Thornborough campaign group.

Group spokesman Mike Sanders said the aim was to save the henges and the ancient burial sites that may lie beneath from destruction. ''North Yorkshire County Council has repeatedly demonstrated that the uniqueness and outstanding heritage value of the landscape around scheduled monuments is of little value compared with income-generating mining,'' Mr Sanders said.

But county council archaeologist Neil Campling defended the previous studies that had been carried out and said all the finds had been recorded properly.

He added that the campaign group was exaggerating its case.

''One particular village, Nosterfield, is almost surrounded by quarrying, and that's a serious issue in itself,'' he said.

''But as to the archaeological issues, they are overstating their case. Various features, such as solution holes where the gravel falls down, give the impression of more destruction than there actually is.''

He said in the event of an official planning application being submitted, a review of the environmental impact of the plans would be carried out. But Tarmac spokeswoman Vicky Fletcher denied the site was under threat.

''The Thornborough Henges site is an important site of archaeological interest and we believe that in Tarmac's care, it is in safe hands,'' she said.

''There are no plans to dig up or destroy the henges and we would restore the site in consultation with archaeological experts and provide a visitor centre.''

The BBC's Time Flyers episode, which will look at the archaeological aspects of the henges, is to be screened on BBC Two on Tuesday November 4 at 7.30pm.