CONSERVATIONISTS are warning that millions of pounds will have to be spent on saving one of the New Forest's most historic buildings from coastal erosion.

English Heritage has cordoned off part of the beach beside Hurst Castle following major damage to the sea defences, which it says are now in a "precarious" state.

The fort in Milford on Sea, part of which is almost 500 years old, is at the end of a narrow spit which juts out into the Solent.

David Hedges, the organisation's head of heritage, said: “Hurst Castle’s extremely exposed location poses considerable conservation challenges.

“Repair work to the sea defences will begin shortly and we're in the process of planning the best approach for conservation work to the castle itself."

The outer wall of the fort is only a few feet from the water.

Mr Hedges said: "Being so close to the sea means the castle will always be vulnerable and climate change will present an increasing challenge for its conservation, but as a charity we are working hard to develop a long-term solution.”

Representatives from English Heritage and the Solent Protection Society (SPS) are due to meet next Tuesday to examine the problem and discuss potential solutions.

SPS chairman David Sizer said work costing as much as £3m could be needed to safeguard the castle's future.

He added: “The current situation is very serious because 80 to 100 metres of shoreline on the south western side of castle are badly eroded.

“Parts of the castle previously underpinned by the shale are now left exposed and unsupported. If nothing is done the castle will in time be submerged into the sea."

An English Heritage spokesman told the Daily Echo: "Over the coming decades the stability of Hurst Castle could be at risk from coastal erosion.

"English Heritage is working hard with its partners locally to manage this challenge."

The oldest part of Hurst Castle was built between 1541 and 1544. Its job was to guard the Needles Passage, the port of Southampton and the growing naval base in Portsmouth.

It was also used as a prison and famously housed Charles 1 before he was taken to London for his trial and execution.

Hurst Castle was enlarged in the 19th century and played an important part in protecting one of the most heavily defended areas in the world.

It also saw service during both world wars and despite its age was used by the military until 1956.