THE future of a rare and endangered species of butterfly has been assured by a ground-breaking conservation project at a Durham coastal beauty spot.

The Durham Argus was in danger of dying out as its colonies on rough grassland areas of the county's coast were slowly eroded by the sea and intensive farming methods.

However, its prospects have been made brighter by strenuous efforts over the past 12 months to reclaim its natural habitat.

The £10m Turning the Tide initiative, a partnership involving local authorities and conservation groups, will unveil the results of its toils in September.

The scheme aimed to completely rejuvenate an 18km stretch of coastline, clearing it of the pollution left behind by mining and heavy industry.

But safeguarding the Durham Argus is likely to be considered one of the most significant achievements of the project.

The butterfly, also known as the Northern Brown, has distinctive brown wings with orange tips and silvery spots on the underside.

The two largest colonies in the country were established either side of the Castle Eden Dene burn, at Castle Eden on the Durham coast.

The most important element for the continued survival of the species is the existence of helianthemum, a plant suited to the area's heavy clay soil. The plant, otherwise known as rockrose, was an abundant source of food for the Argus's caterpillars. But erosion and the colonisation of the grassland for arable farming left the plant and the species in short supply.

Turning the Tide set about redressing the balance in 100 projects in a five-year programme along the Durham coast.

Volunteers cleaned beaches, removed colliery spoilheaps and created cycleways and footpaths.

A spokeswoman for the project said: The butterfly's habitat was being eroded because of coal tipping and spoil dumping.

"Rockrose can only grow wild on clay soils above magnesian limestone, and at one time it was flourishing in the Castle Eden area. The project succeeded in encouraging the spread of the plant and in doing so reclaimed the butterfly's natural habitat."

The Durham Argus is the only species of butterfly which is exclusively found in this country and has not migrated across from the Continent.

Its colonies mainly exist in County Durham but it can also be found in a few scattered locations in Scotland.

Mr Geoff Barber, conservation officer with English Nature, one of the partners in the project, said the scheme had produced valuable results.

He added: "We have safeguarded the future of the Durham Argus, which is a very important species because it is the only one endemic to Britain."