The island was most recently offered for sale or long-term lease through Strutt & Parker, with a guide price in excess of £3 million, before being quietly taken off the market.

Thorne Island presents a rare opportunity to acquire an entire 2.49-acre (about 1 hectare) private island off the coast of Wales, complete with a 19th-century fortified structure adapted with modern amenities for private residential use.

Location

The island lies off the south-west coast of Wales, in Pembrokeshire, positioned directly at the entrance to Milford Haven — a long, deep natural harbour that cuts inland from the Atlantic. Facing the Irish Sea and the Atlantic approaches, Thorne Island occupies a strategic position on the far south-west tip of Wales, in one of the country’s most coastal and rural regions, known for its cliffs, beaches, and working harbours rather than resorts.

A Victorian Sea Fort

At the centre of the island stands a circular stone fort built between 1852 and 1854, now Grade II* listed. It was constructed during a period of heightened concern over a potential French invasion under Napoleon III, forming part of a wider defensive network designed to protect Milford Haven and the Royal Dockyard at Pembroke Dock. Although the fort never saw combat, its position reflects the historic importance of the waterway it commands.

From Defence to Private Ownership

Following decommissioning, the fort was converted into a hotel around 1947, before passing through various owners and periods of decline. In 2017, the island was acquired by a British technology entrepreneur, who undertook a comprehensive conversion that preserved the fort’s structure while installing modern utilities to make the property suitable for year-round living.

The Accommodation

Today, the accommodation extends to just over 8,000 sq ft (about 744 sq m), arranged entirely within the original fort structure. The property includes five principal bedrooms, multiple bathrooms, generous reception spaces, and a sea-view office created from a former lookout position. Original architectural features such as exposed brickwork and vaulted interiors remain prominent, while the roof has been adapted to include a panoramic bar and games room overlooking the surrounding coastline.

Living Off-Grid

The island is equipped to operate entirely off-grid, with a solar photovoltaic array, 100 kWh of battery storage, air-source heat pumps, and an extensive rainwater harvesting system providing about 250,000 litres (about 66,000 gallons) of storage, treated via reverse osmosis. Waste is handled by a modern Klargester sewage treatment system.

Access and Setting

Access is by boat only, via a private jetty, with five sea moorings and a 10-metre (about 33-foot) hydraulic crane for handling boats and supplies. For business-rate purposes, Thorne Island is currently registered as Hotel & Premises, reflecting both its historic use and its flexible potential, subject to planning and conservation constraints.

Situated within the Pembrokeshire Coast National Park and protected as both a Site of Special Scientific Interest and a Special Area of Conservation, Thorne Island offers a highly unusual blend of history, isolation, and infrastructure — a fortified island property already adapted for private living.