Britain's ancient woodlands were once home to a profusion of butterflies but now many forest areas have become neglected and woodland butterfly numbers have tumbled.

The pearl-bordered fritillary is down by two-thirds over the past 30 years while the Duke of Burgundy is down by a half.

The launch of Save Our Butterflies Week 2007 sees the announcement of Britain's biggest ever butterfly conservation project, aimed at reversing these downward trends.

The South East Woodlands Project is being made possible by a £289,000 Heritage Lottery Fund grant and £200,000 from the Tubney Charitable Trust.

Total expenditure on the three-year scheme, to be run by the charity Butterfly Conservation, will be close to £900,000.

Three woodland landscapes will be used to demonstrate how correct woodland management can reverse wildlife declines - at Rother Woods, near Rye in East Sussex, at Derge Woods near Canterbury in Kent and at Tytherley Woods on the Hampshire/Wiltshire border.

Project manager Dr Dan Hoare said: "We want to show woodland owners what can be achieved and how they can help butterflies and other wildlife on their land. We'll be involving the public in a big way so that they will be able to press for good woodland management. They'll be able to go on guided walks and attend events and training workshops.

"We are really grateful to Heritage Lottery Fund, the Tubney Charitable Trust and all our other funders who are making this possible."

Rod Leslie, head of programmes at Forestry Commission England, said: "The decline in rare woodland butterflies like the pearl-bordered fritillary has been one of the greatest biodiversity losses over the past 30 years and reversing the decline is a key objective. This project is an injection of hope for these beautiful and popular animals."