A primitive breed of domestic sheep has been called in by conservationists to tackle the growing problem of bracken.

A small flock of Soays will be expected to eat their way through the fern, which has spread across the slopes above the Derwent Reservoir in County Durham. The fen and heath habitats have over the years been disappearing under a sea of bracken.

The Swaledale sheep which are native to the hills and farms of the North Pennines steer clear of bracken.

But Soays, which are descended from a population of feral sheep that live on Soay, in the Scottish Western Isles, like feeding on bracken stalks.

The fern is a hard plant to control and normal methods - such as using chemicals or trampling by cattle - have been ruled out on water quality and safety grounds.

Andy Lees, the North Pennines Area of Outstanding Natural Beauty Partnership's conservation officer, said: "Our plan is to slowly reduce the area of bracken which dominates the slopes with a combination of annual cutting by tractor-mounted topper and the introduction of Soay sheep.

"Sheep and cattle do not eat bracken as it is poisonous to them, however Soay sheep are known to chew the base of the bracken stalk for some unknown reason, and this helps keep the plants at bay."

Fencing has been erected to keep grazing animals in and contractors started the long-term work of bracken control by undertaking the first year cut this August.

Very few sheep will be introduced at first, but as the bracken reduces in extent and other palatable plants recover, more sheep will be able to graze the site.