A TV archaeologist has accused a council of destroying the landscape around one of Britain's most important prehistoric sites.

Thornborough Henges, near Ripon, North Yorkshire, has the greatest concentration of late Neolithic and early Bronze Age henges - circular monuments - in the country.

It also represents the largest prehistoric quarrying operation in Britain.

Construction firm Tarmac has proposed extending its activities in the area.

But Dr Mark Horton, a presenter on the BBC's Time Flyers programme, has spoken out against the plan - and criticised North Yorkshire County Council over the "destruction of the landscape around the site".

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

Dr Horton said the North Yorkshire council had permitted Tarmac to quarry in the area in 1994 with "only a very limited archaeological survey".

Nosterfield Quarry, in Thornborough, produces more than 500,000 tonnes of sand and gravel each year, but existing reserves are expected to run out within three years.

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 already 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.

But county council archaeologist Neil Campling defended the previous studies that had been carried out.

He said the campaign group was exaggerating its case and that if an official planning application was submitted, a review of the environmental impact of the plans would be carried out.

Tarmac spokeswoman Vicky Fletcher denied the site was under threat.

''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," she said.

* The Time Flyers episode, which will look at the archaeological aspects of the henges, is to be screened on BBC2 next Tuesday, at 7.30pm.