THE boundaries of two national parks could be extended, after the Government's conservation agency announced today it was re-starting work to identify possible new areas for protection.

Natural England said there were large areas between the Lake District and the Yorkshire Dales National Parks which were worthy of landscape protection, but not currently formally protected at a national level.

The agency has re-started its work on designating new boundaries, which could include landscapes such as the Orton Fells and the fells from Shap to Whinfell, in the wake of the decision in favour of the South Downs National Park.

The findings of the inspector conducting the public inquiry into the South Downs supported the designation of a national park which covered different types of landscape.

Natural England said the clarification of legal uncertainties backed the agency's approach to designating areas for national protection.

It now wants to progress with work to extend the boundaries of the Lake District and Yorkshire Dales ''quickly, but thoroughly''.

Natural England will consider a number of areas in Cumbria and Lancashire between the two national parks.

Poul Christensen, acting chairman of Natural England, said: ''I am delighted that our work in reviewing parts of the Lake District and Yorkshire Dales National Park boundaries can now continue.

''It is fitting that as we celebrate 60 years of National Parks - and all that they have achieved for people and wildlife - we now have a unique opportunity to look at a major expansion of two of England's most cherished protected areas.''

The areas under consideration are Birkbeck Fells to Whinfell; Helsington Barrows to Sizergh Fell; River Kent and around Levens; Orton Fells; Northern Howgill Fells; Mallerstang and Wild Boar Fell; Middleton, Barbon and Leck Fells; Firbank Fell; Lower Lune Valley and adjacent fells to the west; Kirkby Lonsdale area, and the area around Cold Cotes.

The conservation agency insisted it would be holding a full public consultation on the inclusion of new areas, and that any decisions would be subject to approval by the Environment Secretary.

The Lake District, which at 885 square miles is England's largest National Park, was designated in 1951 and attracts some 22 million days of visits a year.

The Yorkshire Dales became a National Park a few years after the Lake District, in 1954, and covers 680 square miles straddling the central Pennines.

In some places their boundaries are just a few miles apart.

This year marks the 60th anniversary of the legislation that allowed for the creation of the National Parks.

More than 60 years after it was first proposed, and after much legal wrangling that led to a reopening of the public inquiry into it, the South Downs got the go-ahead as a National Park earlier this year.

Tom Oliver, head of rural policy at the Campaign to Protect Rural England, welcomed news that the parks' boundaries could be extended, and that the proposals would be subject to full public consultation.

He said: ''There is increasing recognition that our outstanding landscapes are profoundly important for our well-being and for the nation's success in the future.

''This decision by Natural England is a clear signal that beauty is a big idea.

''Beautiful places deserve respect from developers and support from Government. Everyone will benefit from this: residents; visitors and businesses alike.''