From the beach far below walkers can see the slick damp of shale and the clean bright Purbeck stone newly exposed by the last landslip: mercifully they can't see hundreds of tonnes of battered Georgian masonry piled up a few feet from the edge, ready to go over the cliff in the next storm.

For over 170 years the Clavell tower has been a landmark perched above Kimmeridge Bay on one of the highest ridges of the Dorset coast, a World Heritage Site. The tower near Swanage still looks magnificent from a distance. It was where Thomas Hardy courted his first girlfriend, Eliza Nicholl and it inspired PD James' novel The Black Tower.

In Edwardian times the cliff was far enough away for a horse and carriage to drive right around the tower. Now only a few bunches of sea kale separate it from the brink, while the tower itself, gutted in a fire in the 1930s, vandalised and robbed of much of its carved stone decoration, is crumbling as fast as the cliff.

The Heritage Lottery Fund has just agreed to pay for the bulk of a solution as drastic as the problem: to dismantle the entire structure and move it 25 metres inland, at a cost of around £710,000. Engineering reports suggest this should safeguard it for the next two centuries.

The tower was built in 1830 by the Reverend John Richards Clavell, a younger son who had inherited the ancient Smedmore estate, which still owns the cliffs and surrounding fields. Descendants who still live in the area joined the campaign to save the tower.

The Smedmore estate has given a long lease to the Landmark Trust which restores architectural curiosities lets them as holiday accommodation. The trust still has to raise about 20% of the cost, but hopes to start work in spring. PD James gave part of the manuscript of her novel to a fund-raising auction.